Great feedback, thanks. That's exactly what I was looking for.
A lack of healing would be a big problem, I agree. If the players take that route, I toss a couple of healing potions into their pack. Nothing makes them wish they had a Cleric quicker than a dwindling supply of potions
I've found players in Conventions are strange beasts. Everything, but everything, it a legitimate target. Forget about allegiances, friendships or even kinship. If it's got no legs, two legs, four or more, they just want to kill it dead. Cons aren't places for politics. I think you've found that the hard way! I ran a Call of Cthulhu game at a Con once where I uttered the memorable line "My God. You've killed the librarian.........." That was my baptism by fire as to the nature of Convention play. Ouch.
On to the comments............
I'm glad that char gen, skills and combat went well. That's a huge relief! I'd hoped that M20 would work well in a Con, and it's good to see the key elements doing their stuff, especially with a crowd of non-D&D'ers.
Magic was bound to be controversial. People just don't like losing Hit Points. It hurts. That works for my game, but for others, perhaps not so well. Here's an alternate rule to toss into the pan:
As an alternative to using Hit Points to fuel spells, give Magi and Clerics a Magic Point pool equal to their maximum Hit Point total. Spells are cast using this instead of Hit Points.
The Magi or Cleric can use their own energy to power the spells; the Spell Cost is double normal and taken from Hit Points. This loss cannot be healed magically and is recovered after 8 hours rest.
Example
Max is a Magi-1. He has STR 10, 16hp and 16 Magic Points. He casts 5 Magic Missiles for a total of 15 Magic Points. In desperation, he casts another one against the foe; this costs him (3x2) = 6HP. He’s down to 10hp and 1mp. Best of luck, Max.
I've added this to the Macropedia
here.
Regarding the weak mage point; that's intrinsic to D&D itself. Only an alternate magic system (of which we have many now) would solve that bugbear, methinks.
Many thanks, Kensanata!