Last week I made a decision which indirectly led to the death of a character, and I'm not sure if I made the best decision (being a little jet-lagged).

The psion was in a web spell. He wanted to use matter agitation to burn the webs away, but I ruled that it wouldn't be possible to directly agitate the webs, since the strands of silk weren't thick enough to catch fire.

I was anticipating that he would use the power on his spearhead or his cloak to produce actual fire, but he didn't. A couple of rounds later he was killed be a couple of flaming arrow bolts which hit him within the web (and he failed both his saving throws).

Should I have let matter agitation set fire to the web? Or did I make a reasonable decision here?