2012-06-16 by shaenon on June 16, 2012 at 12:01 am Chapter: Choose Want the original art for this strip?
Twelve retries.
There were at least fifteen on-panel and during the seventh he mentioned that he had died fifteen times by that point.
You got pretty close! The only on-panel one you missed was
http://skin-horse.com/comic/todays-comic-953/
This strip mentions the last time they were “dissolved by sewer acid” which was never depicted on panel:
http://skin-horse.com/comic/todays-comic-997/
So I think the total directly depicted is 14.
To be fair he had some time to think it over…