Neutered boars are much the same as uneutered ones, except they are lucky enough to be able to live with sows. They would still live with a partner they were getting on with previously, but any new male-male introduction is still likely to result in fighting. Neutering is not of any use to patch up a shakey pairing either. A neutered boar might well accept a baby boar as would any other boar, but whether it worked long term would still be down to how their characters interact when the baby grows up.
It seems to me that it would not be fair making the boar go through the op and not to let him at least get a sow at the end of it. Cos boars really do love their sows

Purrrrrrrrrumble.