Looks like the answers (except Kagemusha's, to some degree) are based on the assumption that the story the Greeks and Macedonians brought home and was eventually retold by Greek historians is pretty much how it happened. Do we have any particular reason for believing their story? Have we any reasons to doubt it? Are there any sources that tell the story differently? Seems to me that those are the sorts of questions one has to deal with in order to evaluate claims that he lost the Battle of the Hydaspes. To be honest, I wouldn't know where to start.