Alternate Arena Deathmatch Challenge

[Avista]

In a campaign I ran awhile back that was never finished, I came into a roadblock that I never had a chance to find an answer to. If I play the campaign again or use a similar tactic and come up with a similar result, I'd like to have a backup plan.

Background:
The party (4 people) were to overthrow a city of brainwashed denizens. They had the counterspell for the mind control, but it had to be cast by a member of the royal family. The queen was the only member who had managed to survive the initial attack, and she had barricaded herself in the castle, using her own magic to maintain telepathy with surviving rebel fighters on the outside. The rest of her family were either killed or compromised, controlled by the enemy.

Long story short, the party was captured but two members escaped. Originally I was planning to have all 4 members participate in a deadly game of capture-the-flag. If all members of the party had managed to escape, I would simply allow them to continue working their way toward reaching the queen. I did not expect half the party to be captured, and the other half to remain free.

With that explanation in mind, what kind of arena deathmatch could I run with only 2 people? I wanted to avoid a regular fight. Or as an alternative, how would you have progressed the story?

Edit:

I should also mention there was an NPC with them who got captured early in the session - the prince of the family. He was going to either a) be a sidequest rescue by the party or b) become a miniboss before they got to the queen. Since they did not take the sidequest and rescued the prince, he was going to be a miniboss. I was not eager to pit only half the party on the prince. I would have to nerf him, and they would probably notice that.

[Quertus]

Why "deadly capture the flag"? Because the evil overlord thought that it would be entertaining? Well, what would he find entertaining with 2 PCs? Summoning 2 monsters to be "on their side"? Making them as much a mockery of the two that got away as possible? (Letting the two players play their mockery, so that they're not just sitting there bored?) Or some other game entirely? (Which only involves the two PCs, but might bore the other two players?)

What was the win condition for the 4 captured PCs? Does that translate well to just 2 PCs?

What would the other 2 PCs be doing during this? (Would it take much game time, and would the other 2 players get bored?)

[Avista]

Why "deadly capture the flag"? Because the evil overlord thought that it would be entertaining? Well, what would he find entertaining with 2 PCs? Summoning 2 monsters to be "on their side"? Making them as much a mockery of the two that got away as possible? (Letting the two players play their mockery, so that they're not just sitting there bored?) Or some other game entirely? (Which only involves the two PCs, but might bore the other two players?)

What was the win condition for the 4 captured PCs? Does that translate well to just 2 PCs?

What would the other 2 PCs be doing during this? (Would it take much game time, and would the other 2 players get bored?)

The opposing force was an army of mindflayers, and since they were unfamiliar with surface-dwellers, they wanted to experiment by putting these uncontrolled captives in a situation so they could study them. Since I was still relatively new to D&D in general, I wanted to avoid separating the party and running two scenarios simultaneously. I was very new and all. (Since I have more familiarity now, I could probably pull it off)

I had three win conditions in mind: they figure out how to escape the caged arena they were in, (arena was originally a large theater with a trap door leading out that the mindflayers didn't know about), they overpower the guards that exchanged players, steal weapons and fight their way out, or played so well the leading commander, a non-flay, invites them to his private quarters and proposes to extend an alliance to them. They could proceed to agree to the offer, murder him, escape, or whatever they chose.

With only two PCs captured, I didn't know what to do with the other two. I don't want to force them to save their friends, because maybe they would have thought it to be better to get the spell to the queen and free everyone in the process.

I should also mention there was an NPC with them who got captured early in the session - the prince of the family. He was going to either a) be a sidequest rescue by the party or b) become a miniboss before they got to the queen. Since they did not take the sidequest and rescued the prince, he was going to be a miniboss. I was not eager to pit only half the party on the prince. I would have to nerf him, and they would probably notice that.

[Koo Rehtorb]

Put those characters on ice to be rescued (or not) at a later date. Give those players a couple of resistance fighters to play in the mean time.

[Avista]

Put those characters on ice to be rescued (or not) at a later date. Give those players a couple of resistance fighters to play in the mean time.

I guess that's one option, but not one I'd be eager to use.