doctorbadwolf
Heretic of The Seventh Circle
I think it's fine to use combat encounters as long as you cannot take a short rest between them. Perhaps you can choose to increase the DC of a check in order to still make the check and get a rest, but that risks another resource draining obstacle. And I wouldn't make them fights that will last long, make them glass cannon fights that hit hard by where team monster has small HP numbers.I agree with the others that the failures shouldn't lead to combat encounters. 4e doesn't do "time-wasting" encounters very well. So random encounters are just something I'd avoid.
I'd consider having the cost of failures take away Healing Surges or other resources.