What are the possibilities of increased malfunction or failure in guns built with mag safeties, which have them removed/disabled. Is this advisable? Dependant on the gun? (Say P320 for the sake of example)

Most guns are designed with them as an afterthought. I work for a major manufacturer, and we see more issues WITH the disconnect (given, it's mostly just CA guns that have them).

My Bersa Thunder had one.  It's a cheap little spring.
Since it flew away the gun has functioned 100%.

Some folks (and gunsmiths) get all nervous about the subject of disabling any safety features from a liability standpoint . I consider a magazine safety to be of dubious value from a safety standpoint and would not worry much about it . If you handle the firearm properly a mag safety should not really come into play .

Could however be some liability if you were to sell the pistol . Best bet would be to save all the parts and reinstall if getting rid of the gun

With a very few exceptions these are not safeties.  They are magazine disconnects.  The only example that i can cite off the top of my head of a true magazine safety is Seecamp.

Some fool will pop the mag and assume the gun is now 'unloaded.'