What would have the Prophet (saw) done if people from his Ummah were getting harmed?
None of us truly know the answer to that question. Being a prophet, my guess is he probably did as Allah instructed and those instructions were probably dependent upon situations and on things unseen that Allah knew that humans did not. In general, of course the prophet is going to do something about people being hurt, but exactly what he would do, when, and how depends upon what the situation was and what instructions were received. If you are wondering why the next messenger, Mahdi, hasn’t stepped forward to do anything about what is happening in Palestine, try to remember 2 things: 1. Allah tests us and ordinarily doesn’t send a savior to rescue people from warfare, millions have died in wars with no Mahdi showing up to put a stop to it. 2. It is Allah’s plan, not Mahdi’s, so try not to blame him for being late, he is probably just as anxious as anyone else for him to be in a position to bring an end to war and injustice, even if it is only for a little while.
