Eric:

I'll throw in my 2c worth just to get the discussion started. I think you did the right thing and can leave it indoors until after last frost next spring. Pomegranates are listed as 100-200 hrs chilling. Not sure that has anything to do with it but low chilling stuff like that often doesn't realize it missed winter. So yours will have a really long summer and carry on next year.

Putting it outside without established roots might kill it.

Let cutting grows inside throughout the winter is what I will do.
In zone 5, I grow Pom in the pot. I bring it in when leaves all fall off. Then put the pot in unheated garage. The tree looks like dead but when it sees the sign of spring, it will send out new leaves in no time...
However, I have a dwarf ornamental type Pom, nana, that grows like evergreen inside under house temperature.

I agree with fruitnut. The chill hours would matter more if it was going to fruit. Just make sure it does not dry out and it will get a jump start on next spring.

Thanks, everyone, for the advice. If it will tolerate an extra long growing season, that sounds great. Thank again.