Astral Seed + Fusion

[Zanos]

Your astral seed produces a copy of the fused being, with all its abilities, stats, and so on. Since fusion generally grants control to the manifester, presumably the astral seed clone is under the manifester's control. Ask your DM, though--the problem of determining control has been used to shut down the fusion + astral seed combination.

This is a relatively long argument but abilities should include their durations. So the fusion would still expire after however much time was left in it when you cast astral seed. You'd then have two copies of the fusee.