There are two similar expressions:
1) (Ε,) τι να γίνει;... = What can be done? (The question is rhetorical, usually)
Ex.:
-It has been raining for 5 days in a row!
-Εεε, τι να γίνει... This, too, shall pass...
2) Τι θα γίνει;
Like Acestor showed at the end of their message, this is usually said when the speaker is irritated/annoyed because the other person keeps doing something that the speaker considers to be wrong. Expanding on Ancestor's example a bit:
-Good morning, boss, sorry I'm late.
-This is the 2nd time you're late this week! Τι θα γίνει; Will you keep doing that? Do you want me to fire you?