Not really, Feledren being hit hard by the blight just means its terrible land for Orlais to hold. It will cost the empire far more than they gain to reconquer Orlais1,2,3. The currently Nevarrian leader is old but its unclear just how much control their mage order has nor is it certain how quickly a new leader would emerge. 4,5.Nevarra is the power it is today from successfully challenging the Orlesian Empire so it would be wise not to underestimate them.
1.Fereldan has rich sea trade, holding the province was made feasible due to that originally and that was what will make the reconquest worth it.
2.Fortunes will be made, just as they were in the original war.
3.Not to mention it is sitting on a literal mountain of lyrium near the border
i'd say that's worth the invasion right there.
4.Were you not paying attention to the part were Nevarra rule became unpopular in the western edge of the country, namely what they took from Orlais in their prior confrontation in 8:70 blessed. You cannot rule a country when it finds leadership to another more appealing, beyond that if the secession crisis was clear cut, it wouldn't be a crisis.
5.The only direct heir to the throne doesn't want it.
Ultimately Fereldan it self isn't worth much, but its placement on the map makes it valuable.
And Nevarra can challenge Orlais if it wishes, i will wish them good fortune if they do.