i think you are talking about a returning player complaining, not a new player / promises, right? if so, the returning players leave very rarely, and you can mostly ignore those messages. on rare occasion, one will quit though. so if you really would be upset about it, you can do something, but perhaps 1 of 50 will quit if they complain and you ignore it. it kinda sounds like the extra minute or so didn't make a difference, and the guy is still gonna be about 2% to leave (just like if you ignored it). but it could be less likely than that. 10mpg is pretty much for a senior to quit, it would probably be 1-2% at 0mpg. we are just talking so low odds its impossible for me to say if that 10mpg makes a difference or not.
but long story short at least 98% chance the guy comes back?