I'm conflicted on this, on one side I find it extremely annoying that Bioware had to put the Warden's fate in such an unsure position again by playing the ''mysterious disappearance'' card with Leliana, especially if they don't intend to use it in DA:I.
On the other hand, Bioware's trend of characters disappearing and no real closure, is because they want us to use our imagination to decide for ourselves how our characters ended up, like Hawke and The Warden.
Again, if Bioware has no intention of doing anything again with the Warden, they should not have mentioned him/her the way they did in DA2, sure, references to for example Mahariel being the ''Hero of Ferelden'' by Merril are fine, but not important things that put the entire fate of the character into unsure territory again, all for a long off ''maybe'' in the back then DA3 concerning The Warden possibly being in it in some way.
Anyway, to some, like me, something like this means a lot, while others, like the poster above me, couldn't care less about either one of the previous protagonists.