How long before Apple kicks them out of the apple store? I thought Apple always had a policy of limited tolerance toward xamarin (after having banned them once). Isn't them becoming MSFT a casus belli?
Which is why I expect MS to make Xamarin available for free, and push it quite heavily.
The only thing you can't do is issue new code by bypassing App Review (except web pages / web apps) or have your own non-sandboxed JIT.
They could have succeeded against Xamarin, but not Microsoft Legal.