They won't be able to. The Gaza strip was densely populated with a large number of apartment complexes. Those can't just be rebuilt.
The Gaza Palestinians still alive are either currently living out of tents with the hope that the bombings will eventually stop so they can have the opportunity to live in whatever gets built (they likely won't) or have already seeked refuge in another country.
Also, none of this is new. It's been happening for 80 years and has been in planning for over 100.