First of all, thanks for the advice and encouragement.
To sum up, ds was weaned at 4 1/2 months to Neocate because of silent reflux and allergic colitis which did not improve with elimination dieting. At 6 months old I started pumping to relactate. The first day I got a teaspoon total for the whole day. On day 24 I got 16 oz!
Two days ago we switched back to breastfeeding. I wasn't sure ds would want to latch on, but after a few seconds of crying he latched on and he's been nursing ever since! He's been frustrated in the afternoon/evening when my supply is low but hopefully it'll finish building up soon. I haven't given him any supplements, other than a few sips of water when we were outside in the heat. He is having enough wet diapers, though they aren't as wet as I'm used to seeing. He'll be 7 months old in a few days and was drinking around 30 oz of formula each day. Once he's used to being on breastmilk again we are planning on re-starting some solids in a couple of weeks (he tried some briefly at 6 months but then we stopped).
He's also fussing as the formula finishes working through his system because it constipated him pretty badly. I'm also prepared for him to still have some fussing from the allergic colitis because I am no longer doing any special dieting. But I'm praying his system finishes maturing soon so we can have a happy nursing relationship from here on out!
Anyway, thanks again for advice, and hopefully by my sharing this I'm encouraging someone else!