yeah you can. you can't replace ryan key, the guy writes the majority of the music. as long as he is still writing as well as he has on their last few albums i would never ask them to call it quits.
i will say that LP is one of the best drummers in a pop punk band and definitely gave yellowcard an energy and level of musicianship that placed them above a lot of other bands in their scene. they'll need to find someone top notch to maintain that quality.