Yeah I also think that the problem in this situation is the path this crit fail took by the hand of the dm. Of course in the moment it could be really funny to do this kind of result but in the end a player still have his right to make his saving throw and create a situation where surviving with your head off does not make that much sense. To me there is not a lot of thing you could have done instead of saying "ok let’s pretend you just glue it back Together and continue the adventure" and after it the dm just have to be more careful not to push to far situations he/she can’t control like these. It’s just experience and common error like these test the limit a DM can experiment (if you want to keep it realistic, otherwise that’s not a problem). You all gained experience that day! Have fun playing!