They've said that S13 starts by showing the brothers' reactions to the finale events. Why do you think Cas dying THIS time affects Dean so strongly compared to the previous times?
Well, this time IS different.
It’s 6 years since last time he was dead for a long time (and they’d only known each other 2 years by then, now it’s been 9!) and 4 years ish since he was stabbed but brought back immediately. Of course there are bits in between but they’re not quite the same, purgatory for example, Dean thought Cas was probably gone but he didn’t see him die before his eyes, but he DID see him fall away before his eyes and it was so emotionally awful he made up a whole other scenario in his head…
So yeah, time getting to know each other + the fact that imo they both realised they loved each other around s8/9 + Dean has literally just been trying for the last 2 years to somehow tell Cas he loves him and wants more but is an emotionally stunted idjit + Cas literally just told him he loved him + the fact that this is the first full angelic death they’ve seen of Cas, it LOOKS final + everyone else dying / being taken away too…
It’s a lot to process.
So yeah, IMO we should see them really coming to terms with his death but… of course not in the same way due to their relationships with him but also it appears Sam is positive about getting Mary back while Dean isn’t. It wouldnt surprise me if this time it’s again SAM who is all “don’t worry he’ll come back Dean he always does” and DEAN who is so shocked and traumatised by it all that not only does he think Mary is gone for good but also Cas.
It doesn’t really make sense to have what we know of Dean’s grieving so far if he doesn’t KNOW Cas is gone for good in his heart.
It also doesn’t really make much sense to kill Cas off in such a ‘spectacular’ and final looking way if not to capitalise on it by making them believe he is gone for good.
Why would Dean be SO grieving, praying to GOD, BARGAINING, wanting to shoot Jack in the face, having a massive break down…. these are not the things done by someone who thinks the person they love is likely to come back you know?
The death of course is important to Cas’ own story and I think we are getting his arc here, but even Misha said it was extremely (even, he said more, but that’s his opinion so far with what they know, they’ve not filmed it all yet) relevant to the boys. Which means they must think he is dead for good.
If you thought season 7 was depressing… but the thing is Dean has changed since season 7, he’s more open now, in season 7 we had SO MANY good moments of Sam wanting desperately to get through to Dean, trying to get him to open up and now Dean in theory should do so after his character growth.
There will be mirrors of season 7 I’m so sure, but they should also be flipped now, with Dean’s character growth showing through (though probably not til after the breakdown, when he then picks himself up and does open up).
Then we also know that Sam is the one holding it together, but he will probably break down later in the season from what Jared said, and that makes sense because it will be so much for him too, all this, he also loved Cas, even if he didn’t have the same relationship as Dean did, lmao Jared, but yeah, plus Mary, Eileen and all the Jack / Lucifer story, of course it will all add up and lead to big things for Sam too, but the early season IMO will be heavily Dean/Cas focused emotionally.
This is my thinking anyway.