The best person/physician to comment on chances of dying from any given procedure is the person/physician who's recommending said procedure.  Ask him/her what you just did above.  Ask about alternatives and the risk associated with said alternatives.  Don't forget to ask about the risk of dying even without performing any procedure at all.  

With all that said, you need to ask your dad whether life is worth living or not.  I'm not implying that he's going to keel over any moment.  However, some persons who have a lot of medical conditions and require a lot of medications or therapy may decide that doing nothing is a better option than undergoing a (risky) procedure fraught with side effects, not the least of which may be a long rehabilitation & recovery, possibly never to return to their baseline level of function.

This is where his family physician can help in assessing risk vs benefit.  Typically, if you want to undergo a procedure, the benefit should outweight the risk of said procedure and of not doing anything. 

Also, do something because it's going to make a difference, not just because it can be done.  I hate to admit it but I'm not familiar w/liver aneurysms.  So make sure it's really necessary.  Again, this is where his family physician can help bridge the understanding btwn your dad & his surgeon.  

Good luck!