Yes - because...
It's on schedule for planned launch and most of the funds are already spent or committed
There's nothing to take its place
If we send nothing to Mars, we obtain no new data*
* accepted, the existing orbiters and rovers will continue to return more data for some years to come, but each instrument tends to have a peak of "new science" value and then tails off to "more of the same" after about 6 months. I value all Mars data highly, but I value most the data from new instruments and new surface locations.