I don't want you to think I'm implying that you don't keep his water quality in great shape, I can tell from your routine that you do.
It's just that often when treating with antibiotics, traces of ammonia can start to accumulate in the tank; the drug manufacturers often tell you to hold off on water changes until the treatment period is complete and then couple that with the added negative impact, even if minimal, that many antibiotics can have on the beneficial bacteria in the filter and tank surfaces - this can cause levels of ammonia and/or nitrite that you would not normally have in the tank.
Very few of the antibiotics we use for our fish are more effective by allowing them to remain for days in the water, then adding more and then after a period of time doing a partial water change as many products direct.
In this type of protocol ammonia and other toxic substance can reach levels that are counterproductive to the treatment plan, even barely detectable amounts. I talked with a drug rep with Jungle Labs, and another one with API and they both conceded that rising ammonia levels are a problem in those treatment plans.
Those same reps agreed that the best method is to do a big water change, dose the antibiotic, wait 24 hours, do another big water change (huge 80-90 or even 100%) and then dose and keep this up for 7 to 10 days, depending on the med, but the manufacturers don't think the hobbiest will do the huge water changes to remove most of the degraded antibiotic.
I've never used Maracyn Plus, but I understand from the company's product description and from others who have treated popeye, you selected an excellent med for that. I don't know enough about the bioavailability of it in the water for extended periods as compared to most antibiotics which degrade and are unavailable after just a few hours.
Maracyn Plus has what they call "biospheres' that attach to the fish's skin and increase the effectiveness of the drug; I haven't read enough of the company's product information to know if they claim added benefit by a cummulative effect.
At any point, since he seems improved at this point without further antibiotics I think the Betta Revive is a good product and will most likely help and will "do no harm".
I know you're keeping a watchful eye on him and will be able to see any changes, even subtle ones.
As BFM mentioned, Ich is always a possibility, but also watch for any very subtle changes to his body: any surface lesions or patchy areas... dullness... filminess... white-is or grey-ish bits or tufts, even tiny bits between his scales, which could indicate Columnaris is starting.