i just think they should've let jack be a baby for a little while because dean would've find comfort taking care of him while grieving and then when cas came back and they were in the bunker dean would've gathered this tiny lump of blankets, cradling it gently, and gestured for cas to come over, and cas would've walked towards them slowly, afraid of disrupting the moment while taking in the heartwarming vision that was dean, then he would've looked over dean's shoulder and stared fascinated at jack's sleepy face, all pink cheeks and pouty lips. he wouldn't notice dean looking at him with eyes full of love and relief and gratefulness, eyes so soft a tear fell on jack's forehead. cas would pose a silent question, trying to discern dean's emotions. and dean would answer, in a voice as small and fragile as the baby in his arms, 'i'm so glad you're back, cas. i couldn't do this without you' and this... this would mean everything really. especially this baby, this powerful creature contained in a chubby infant who wakes up crying at ungodly hours, needs constant supervision and is a goddamn miracle. this baby that is theirs, from this day to forevermore. they would be good parents to jack, maybe they'd build a loving home where both of them could fit in too. 'i'm glad to have come back to you, dean. to both of you.'
