What is "Oy Mi Yichyeh mi'Sumo Keil" referring to?
Rashi #1 and Ramban: With reference to the various decrees and exiles, beginning with Ashur, Bil'am is woefully exclaiming "Who can survive the decree of Ashur?" 1 - who mixed-up all the nations? Followed by ships from Kitim (Rome), who will exile Ashur, and who will themselves ultimately be destroyed. 2
Rashi #2 (in Sanhedrin, 106a): When Hakadosh-Baruch-Hu places a redemption for Himself (Kevayachol) and pays the Tzadikim their reward in the time of Mashi'ach.
Seforno (citing Sanhedrin, 98b): With reference to the coming of Mashi'ach - 'Let him come, but let me not see him!'
Targum Onkelos: 'Woe to the Resha'im when Hashem does these things!'
Targum Yonasan: 'Woe to whoever is around when Hashem comes to pay the Tzadikim their just reward and to punish the Resha'im; To break up nations and their kings and to incite one against the other'.
Da'as Zekenim (citing Reish Lakish, Sanhedrin 106a): Woe to one who tries to keep himself alive through Shum El (any idolatry) or Alah (curse).
Da'as Zekenim (citing R. Yochanan, Sanhedrin 106a): Woe to the nation that will (be subjugating Yisrael) when Hashem decides to redeem them. Who can stop two lions from mating?!
Da'as Zekenim, Hadar Zekenim (22): Who can live through what Hashem will be Sam (put) in the world (Mashi'ach)?!
Hadar Zekenim (24): After seeing that all the nations will be finished in the days of Mashi'ach, Bil'am lamented 'who will live