I've tried researching on this forum but didn't find as much info as I was hoping for. If a horse was diagnosed with EPM this spring but they were treated and are now recovered is that something that follows them the rest of their life? Continued maintenance or treating it? Would you personally look into buying a horse after being told that? 
Thank you!

Location and exposure is key. Around here all horses have been exposed and "probably" have it in their body like dogs carry red mange. Symptoms only pop through the immune system and show up as EPM on a low percentage. Vets in the Deep South recommend treating for EPM on a yearly basis. I would buy a horse that had been diagnosed and treated, but I would not buy one that had a severe case including muscle atrophy. 

Not a clue but I'd ask the best vet around.  ;-)

Is it a horse around here? I know EPM is very uncommon up here. (not that it can't happen)

The horse is currently up here but spent the last two summers down in TX. 

I have a horse that has been treated repeatedly. I think he had had about three rounds of Baycox snd three rounds of Rebalance over the years. My vet he was getting reinfected NOT relapsing. The last time he was treated was with Torturizil. I don't think that is how you spell it but it kicked butt and I have not treated the horse since.  I tried to find the drug and found Protazil. It was $800+. What I gave was about $200.  I think that has been about 5 years ago. Did follow up with Vitamin E this last time and I think that helped. possums are the main carrier but skunks and raccoons are also. Horses can get it from hay or feed where possums have pooped. My vet and I also discussed cats pooping in the hay. Hope that helps. Altogether I think I have had four horses with EPM. Possums are bad here snd the coins have a party here EVERY night.