It seems the last 3 Ukraine Presidents all finished their term with horrible approval ratings. Yushchenko ran in 2010 and finished in the low single digits. Yanukovych was overthrown in a coup but would have for sure lost by a mile if he ran for re-election. It seems now Poroshenko is meeting the same fate. I guess the voter expectations are just way beyond what the current Ukraine state is capable of generating.
I doubt about Yanukovish tho. He had about 20-30% in all opinion polls until his escaping. He would have lost 2015 presidential elections to opposition candidate (Clichko/Poroshenko), but he definitely would be in the second tour. His situation was different from Yuschenko's and Poroshenko's, as Yanukovish was non-alternative candidate from the East.
I did recall he was polling OK in late 2013 but those polls were done before the 2014 crisis. I suspect after the crisis started there is no way he could be polling that well so even if he survived the Euromaidan uprising he was for sure doomed in any re-election effort. Most likely by a mile.