It is exactly the same risk as all the other CPU's (Haven't lost one yet - 7700K's to 3770K's etc), I have not had the pleasure of doing a 8700K.
The delidding process is very safe it's more the relidding that might not always be successful if I don't have a testing machine to check temps afterwards.
And with that, I mean the application of the thermal paste, so still, it shouldn't just spontaneously combust luckily, because of Intel's thermal throttling.
But as mentioned, I haven't had any issues thus far, nor had to re-delid any CPU.
Of course, anything can happen, and there is no guarantee.