Yes, they should have a long life left... mechanically speaking. From a financial standpoint however, apparently US feels the CRJ-200 and CRJ-700 will get more revenue for PSA by carrying more people.
As Dornier is out of business, spare parts for a fancy ac that only carries 31 passengers was likely becoming a problem. The last flights for the type are mainly PIT
-CAK today, at 13:10, 15:15, 18:15, 20:10 and 20:25. The last one, 2566 PIT
-CAK, has a very light load and is probably the final revenue flight for the PSA 328 fleet.