Add failsafe for exit if we drop events

If we drop events, especially exit events, that process will never be pruned from the cache.
To fix this we need to add a failsafe that triggers when we miss events but is also bound by time, say you lost X events, so somewhere in the next seconds/minutes we manually check if every process is still alive, probably by scraping proc.

Not labeling this as a bug as losing events is very very very hard.