Why didn't Jiraiya use reverse summoning as a way to escape?
Simply said he could have, and Fukasaku even recommended Jiraiya to do this. But Jiraiya decided not to since he already got too close to find out Pain's ability and identity. Also there would be no second chance in finding out his ability after this anymore, because Pain would be more careful afterwards. 


  When Jiraiya originally summoned the elder toad couple they also asked him why he was fighting1. A few chapters after, when Jiraiya already got gravely wounded2 and orders the elder couple to retreats he gives his reasoning for staying




1(chap 376 pag 3-5)
2(chap 381 pag 10-11)