Well it would be hard in a radius because a hero's body dissipates quite quickly.. actually instantly I believe..
You may be stuck with a odd trigger that just instantly revives all the heroes that have fallen at the location of the caster..
Or you could try changing Resurrection's target to hero that MAY work, but also it may require a modification to hero dissipate times..
I'll try it out for ya real fast
be back with results.
Edit:
After some testing.. I'm afraid I cannot come up with a solution.. it seems when a hero dies they do not spawn a corpse.. and therefor as soon as they die, they are removed from the map (but still ingame, as a revivable hero)
So basic abilities will not work regarding resurrecting a hero.
I will however try one more thing to solve this problem.
Edit 2:
I have managed to make a trigger that ressurects all dead heroes that are allies of the player.. but it resurrects ALL of them, not just ones in range =/