I think I've broken the main quest in Shamazaar: I got the Shamaz to come and heal Ilott, but now I can't speak to him at all, but I've spent so long doing other things and now can't go back to an earlier save game (except the one from when I first came into the region). I know I have to speak to him, then Maar, then get a tablet from a chest and give it to the Shamaz, but none of this is happening -- and even when I find the chest in a house and blow it up to get the tablet, the Shamaz still doesn't want to know! Is there anything I can (such as a cheat) to reactivate this part of the main quest, or should I just give up and go back to the start of Shamazaar (several hours' play)? At least if I do that, I can stop riss production more quickly and thus spend less time fighting hard-to-kill guards ;)

***Spoilers***
After getting the tablet, whch Shamaz are you trying to talk to ? You have to take the Tablet to Shamaz Mazum, the one in the temple, so that he can tell you about the symbols.

Tassi is right, I had to start again -- but this time I did it RIGHT! And I can confirm that the main quest was indeed broken before -- Ilott and the guy at the Well of Essence both weren't talking to me before, so did I shoot them by accident, or cause them to be hit by a soldier when they were talking to me? Just so I can avoid this happening again...
And yeah, now I know I was talking to the wrong Shamaz (the one in the village) -- it's better that I restarted, I may have broken other main quest aspects as well... not to mention how much ammo I wasted. Besides, I bought a twon-ha early on this time (and also understand the teleport beacons), so I'm progressing much faster than before. Thanks guys ;-)

I'm not 100% sure you were really stuck, but since you had wasted alot of ammo a fresh restart was probably the best option.
I really don't know why Illot or the other guy weren't talking to you in your other playthough, but yeah, i assume shooting them or letting them get shot probably isn't a good thing ;)
Anyway, save often just in case you run into troubles again. Have fun ;)