There are a few things you can do to keep the high level games playable without ressurection magic.

Firstly there's Revivify - for those unfamiliar with the spell (or psionic power) it basically works like True Ressurection except the casting time is reduced, its available at 9th level but can only affect a creature that has died in the last round (though the psionic version is augmentable to affect creatures that have been dead longer). Keeps death deadly but not an automatic "game over".

Then there's the idea used in Dark Heresy. Characters gain fate points which can be used to re-roll certain dice. Characters could also lower there maximum of fate points by 1 to avoid death. If you're using Action Points or some variation then this idea could be worth taking (alternatively, if you're not using Action points you could just create something like "Life Points" which exist only to be used in this way).