SpoilerNo, that guy is dead even if they didn't show it. He was simply from Braavos, that's all. He drew a sword on Kingsguard knights who were proven to have survived that fight. They wouldn't let him live. Pretty much all the Kingsguard except Selmy were real scumbags in the books.
The only credible rumor about Jaqen is that he was *maybe* in the prologue to Book 4. Because it has a man described with the same look as the man Jaqen morphed into when he parted ways with Arya.
I dont know that it can be outright dismissed although like you said how would he have escaped? Them having the actor who played Syrio stand in as Jaqen at the end of the first season has fueled the theory. I would say Possible but not likely.