Knowing how over the top some Corrie storylines have become, I wouldn't be surprised if Gail is killed off by being murdered by Corrie's latest (possibly soon-to-be) serial killer.
Which would be Joel, who was recently revealed to have been the one who killed Lauren Bolton, and is also sexually exploiting teenage girls.
Gail starts to get suspicious, finds some incriminating evidence, Joel finds out and bumps her off.