It sounds as if you first need to decide whether you’ve permanently bonded with Dax? If you haven’t, then ideally he would be adopted by the woman whose bunny seemed to take to Dax, while you could provide a foster home for another bunny. (I have to say, I have so much admiration and gratitude for you and others who provide foster homes for bunnies. It takes someone really special, and with a huge heart, to provide loving care to the bunnies and bring out the best in them, all the while anticipating you will end up turning them over to other people. The two times I tried, ages ago, we ended up adopting the buns because I couldn’t let go.)
If you and Dax have bonded — if you feel as if it would break your heart to lose him — then in my opinion your decision would come down to whether you’re 100% prepared to keep him AND Runa if it turns out they don’t want to bond with each other, or if the bonding process takes a really, really, really long time.
How long is really, really, really long? So far, in more than 30 years of living with rabbits, my husband and I haven’t had bonding take more than a year (and that was with a trio, under unusual circumstances), but right now we’re about to begin Month 7 of working with two bunnies, Cap and Anna, who definitely want to bond with each other, but are stuck on the issue of dominance. We’re reasonably confident that they’ll come to an understanding within the next few months…but three months ago we thought it would only be a few more weeks, so who knows? We expected six-year-old Cap would demand to be the dominant rabbit, based on his two previous relationships (those partners crossed the Rainbow Bridge), but he was so desperate to regain the bliss of bonded pair life that after less than two months he gave ground and offered Anna a 50-50 partnership. We’d never seen this happen before, so we were amazed and delighted, anticipating Anna would quickly agree. No such luck! Anna is every bit as obsessed with being the dominant rabbit as Cap has ever been, and having spent virtually all of her 3+ years in shelters before we adopted her, she thinks her life now is pretty fabulous and doesn’t understand how much better it could be as part of a bonded pair.
Eventually, either Cap will give in and submit, or Anna will meet him halfway, but they’ve been in a holding pattern now for 4+ months, and all we can do is keep trying different ideas to encourage positive changes. This is the first time in years that we’ve had bunnies take more than a week or so to bond, and we’d forgotten how challenging it is to remain patient and give the bunnies whatever time they need to work things out. (Admittedly, we’re also contributing to the length of the bonding process for Cap and Anna, because we’re not willing to let them harm one another, so they can’t use the shortcut of fighting; he’s 1-1/2 times her size and weight, so she’d be at a distinct disadvantage.)
My apologies for rambling on about my own buns, but being reminded daily for months that bunny bonding can be a long-term proposition, I wanted to encourage you to think about whether you’d be OK if Dax and Runa end up needing a lot of time before they decide to become a bonded pair. With an x-pen panel between them, Cap and Anna are totally relaxed and often lie next to one another. Without a barrier, it’s a lot more complicated! That’s not to say you should expect Dax and Runa to follow Cap and Anna’s pattern, only to consider “what if”.