I wonder if now, after realising how disastrous Brexit may be, he is having a rethink and doesn't want to be the person blamed for a catastrophe for decades to come.

No, I believe he stated his reasons quite clearly in the link you gave:

So maybe, just maybe, I'm reaching the point of thinking that we should have a second referendum on EU membership ; unless you want to have a multiple choice referendum, which would confuse people. I think that if we had a second referendum on EU membership we would kill it off for a generation.

The percentage that would vote to leave next time would be very much bigger than it was last time round. And we may just finish the whole thing off. And Blair can disappear off into total obscurity