What if the Warden has died from the taint by now? How old do we assume the Warden at the start of the game? Twenties, I would suppose, some even like for them to be older, so it could be likely that he Taint overcame the Warden, and s/he died from it, whether they went with Morrigan, or didn't.
if the Warden did go with her, could be very likely that he died in wherever they went, and Morrigan left, possibly from sadness, not sure.
If they didn't, then they left, lived a while, restarted the Wardens, and then went to the Deep Roads, a much more honourable death than the alternate, I think.
Also, if the child thing can be cannon, like if there's an option for which ending you chose, if you can't import your saves, I want to see the kid. Curiosity has me at this point, could be the most powerful thing walking around, could be that the Darkspawn sense it and go after it.