There are times when you have waive quarantine and risk having to treat two guinea pigs; acute pining is one such situation. It can really lower the immune system and impact massively on a grieving guinea pig.
Glad that Solo has pulled through; mutual washing means that the two want to be friends when the chips are down. It is just the kind of gesture you want to see at the start of a bonding!
I would bond whenever you have a day or two time to watch them and if necessary leave them in the bonding pen.
I was in a similar situation in January when newly bereaved Llawen developed life threatening GI stasis on the day before freshly neutered Llelo was coming off his post-neutering safety wait... Sadly in Llawen's case it was much safer for her move back with her feuding sister and her old group in order to stabilise her as quickly as possible instead of trying to bond her with a new piggy.
Llelo was chosen by another sow a little further down my list of potential sow dates and has settled down very nicely, so it was not an outright disaster!