As I commented in the poll I made in the Killian Jones club (link), I feel that Zeus bringing Killian back was too much of a deus-ex-machina move. These are some of the alternate scenarios I've come across or come up with.

I like the idea of finding a lost and forgotten fruit after everyone has given up hope. It'd be reminiscent of BTVS season 2 and the floppy disk containing the soul restoration spell. There are already a lot of parallels between BTVS season 2 and OUAT season 5/5A, and as I'm a huge Bangel fan too I'd love another.

The ghost idea is something I've developed from a oneshot I read recently. In it, Killian is brought back as a ghost who helps other spirits to move on, and can visit Emma occasionally when she misses or needs him. In that scenario the last 2 episodes would be focused on restoring Killian to life, instead of the random Henry-wants-to-destroy-magic story which I disliked.

I also like the idea of Emma giving half her heart (another Snowing parallel, as if we don't have enough! :) ) but I'm not sure how it'd work, without time travel and/or potentially disturbing grave raiding.

I think I'd have preferred the canon if Zeus was a bit more cryptic in his explanations - either saying something like "there is a future threat you are needed to face" (which would then require more of Killian in season 6 than just providing emotional support for Emma) or somehow hinting that Zeus himself is truly a villain and might be bringing Killian back for nefarious purposes.