I have a theory
And its that McPherson, was in on Walter Sykes' plan.
OK, so Sykes was planning this attack for years, he could have found out about McPherson's black balling, and recruited him, which is when McPherson reappeared. Now McPherson would have known about HG Wells, and unless I'm mistaken, her involvement in his plan was unneeded. Sykes needed HG, maybe she wasn't actually meant to go crazy, and try to destroy the world, but she was released for a reason.
McPherson left Artie the Phoenix, so he could survive, and left the pocket watch for him, knowing that he would probably either die, or be bronzed, and he left it, because I think that he regretted what he did. And left it so when the plan happened, if it wasn't stopped, he could try to erase it.
SOTY rules!!