So the ending might be the only thing mass-appealing they may manage for this series, if they can avoid blundering on that.
Also, if a general-entertainment series doesn't end on a happy note, it usually makes things harder for the channel's next series in the timeslot.
Rarely that next series may do well, but it won't ever do as well as the series which did well until the not-happy ending.
It affects the value of the channel's timeslot as well as of the PH's next series in terms of audience-trust ensuring good viewership.
If mass-audience isn't sure of "all ends happily" from start of series through any number of upheavals, then they won't bother to stick through those upheaval tracks.
No serial's story or tracks is usually remembered accurately and in detail after the series is over - at least not by many crores of nonfandom viewers.
So either the channel or the PH or both detrimentally affecting the worth of that timeslot or their next series, simply for a depressing ending that will do them financial harm rather than good, would be senseless, equal to jumping off a cliff without any safety-measure.
The consequent negative result would be foreseeably sure enough that no excuse would be adequate to gloss over the blunder.