Repost about a betta with fin rot?

About a week ago, I asked a question to verify if my betta had fin rot. He's a crowntail, so I couldn't tell right away that his fins were any more ragged than usual. The edges were dark/black and eventually I noticed that they were getting shorter and shorter. I followed the advice given, and now, the dark edges of the fin have become significantly reduced and he seems a bit more active. I'm noticing some small transparent areas on his fins where the fin had been eaten away. I take this to mean he's recovering. Problem, though. During the course of the infection, the poor fellow lost his entire left pectoral fin. He swims a bit awkwardly now, but seems to manage. Will this fin grow back, or is he lame for good?

Male crowntail betta. Water @ 77 degrees Fahrenheit. Filtered 7 gallon tank. He's alone in the tank with 2 mystery snails. Water is changed roughly every 10 days or so (more frequently because of the fin rot, lately). All chemical levels are in a "safe" range. Only natural plants and rocks as decorations.