I'm thinking that if tyrion doesn't die it'll have something to do with varys because there's been a few hints about what's been going on like varys looking concerned throughout the entire royal wedding before joffrey dies, and being the person who told tyrion to get rid of shae, and then shae comes back so I'm thinking he probably brought her back. I don't know whether varys wants tyrion dead or not but I expect some more interaction between them in the next episode or two, especially after the 'I don't forget a thing' line.
Other possibility I can think about tyrion avoiding execution is maybe maergery (or whatever the spelling is) persuading tommen to stop it because she knows tyrion didn't do it, but this is probs not going to happen considering olenna tyrell is probably happy with tyrion dying, and tommen removed himself from the trial process. Only reason I'm thinking this is that there were some close-ups on her reactions during the trial process.
Jaime could try to bail out tyrion but I cannot see that happening. Also I'm not sure whether tywin's decision to sentence tyrion to death was based on the assumption that the mountain was still alive like what is the process in a trial by combat when both champions die?