If the 2 wither storm heads in the bowels are disabled, after around a minute or so, they should re-activate. (Assuming the command block is still intact).

And if this is already a feature, the amount of time it takes for them to do so should be reduced slightly.
I just think the heads are pretty easy to deal with for a final battle.

While that is the case, if the revival time is too low it'll become more a nuisance than anything, and if it's too high they'll never wake up in time before the player defeats the command block. Overall I think this feature would be more annoying than challenging,