Is there any way to stop Google removing apps from the phone?
Hacking the Play app is probably no feasible option. And as Matthew Read suggests, as a system app, it can do what it wants.

The only other options I can think off is using an alternative Android app market.
You can find some here: http://www.howtogeek.com/106175/the-top-5-alternatives-to-the-android-market/