I think it would've been too difficult for them all to escape without any diversion. And I have a feeling that this same stuff happened in Nazi Germany in World War 2, which is what this film is trying to copy.

It was a war of attrition between the Wolverines and the Russians and Cubans.
Earlier the Wolverines were winning the battle of attrition. They would attack and go back into hiding.
That all changed when Col. Strelnikov and the Spetsnaz arrived. As Strelnikov told the group he was a hunter. And he started to hunt the Wolverines.
War of attrition is the worst type of war to fight. You're hoping to wear down your enemy and their resources before they can do the same to you. There was no way the Wolverines could win.
The only way the Wolverines could have won or kept fighting was to replace their dead with new fighters. But they didn't. At Christmas time Mr. Mason told Jed that a family couldn't feed their kids during the winter and wanted to give their kids over to Jed. But Jed said no.
Even Sun Tzu wrote in the Art of War that war of attrition should be avoided at all cost.

Remember when Jed and Matt were talking in that field and Matt had mentioned that some of the wolverines were getting burned out, except for Robert. I believe that they were tired of fighting and knew they weren't coming back after the attack. They were just done with it all.

It was a distraction so the forces would pull back into town, thinking it was a major attack, rather than just two guys making a mess. They realize they're too small to maintain themselves anymore, and they're getting burned out. The brothers know it's a suicide attack.