Rolling 3 dice you would get 1.5 skulls on average, which if taken conservatively is 1. To be able to make the point sacrifice worth it you would need to do 23 points (round to 25) of damage (taking the Deepwurm Drow as the sacrifice as they cost the least in points). This means at a minimum you need to with your one unblockable damage is:
- Destroy a squad figure of 2 taking up 50 points or more
- Destroy a squad figure of 3 taking up 70 points or more
- Destroy a squad figure of 4 taking up 100 points or more
- Destroy a hero taking up 25 points or more
Looking at the numbers here it seems the easiest to get your points back by taking out squads as a hero at 1 life most likely wouldn't be in range in the first place.
To take the analysis liberally take the 1.5, round up to 2, and double the damage/destroyed figures and half the points required listed above. For example you would get your points back by taking out 2 squad figures of a squad of 2 totaling 25 points. Looks better but won't happen on a consistent basis.