Loomis was suppose to be killed off at the end of this movie
After beating Michael to a pulp, he has a heart attack or a stroke (in H6 they establish it being a stroke at least in the Producer's Cut as the T-Cut removes this) and he collapses and his eyes are open. He looks like he's dead. I always suspected this and it was confirmed to be the case coming across this interview here with director Dominique Girard: http://halloweenmovies.com/various-interviews-dominique-othenin-girard/. Skim down to the bottom to the fourth last question and he explains this. Donald Pleasance apparently wanted out of the series at this point. Rather odd considering Moustapha has stated that Donald was up to do twenty-two Halloween movies if he could. Don't know if this was before making Halloween 5 or after it. Must have been after considering he would surprisingly turn up in Halloween 6. The interview is a good read and the director also explains why Michael's mask looks the way it does in the movie. It was made that way to have him appear more humanized.
But anyway, back to the Loomis thing. If you ask me, he should have been killed off and replaced with some one else in Halloween 6. While it was nice to see him pop up again one last time, let's be real. In the film's original version, the Producer's Cut, Dr. Wynn (the man in black of H5) wanted Loomis to replace him as leader of the Thorn cult; which is odd considering Loomis was a much older man and on the verge of death. Made sense if you had a much YOUNGER guy here. Then you had the death of Donald which affected the reshoots because they couldn't film any new Loomis scenes to go with the new story aspects (the whole science experimentation thing at the end) and needed to shoot around his parts. The biggest would be the office scene between Wynn and Loomis and having to have Mitch Ryan read new lines to match Loomis' dialogue from the original version which probably would have gone differently had Donald been alive. Then you have most of his scenes being cut out from the theatrical cut anyway, making it a waste of Donald to even be in the movie and barely having much to do especially in the third act.
So yeah, it was quite a mistake having Loomis in Halloween 6 and should have just been left dead at the end of this movie. It was quite odd to see he even survived since I don't know anyone who has a stroke and collapse with their eyes still open.