Well I suspect he will not kill her off, might make game to dramatic after what already happened and he seems to like her too much.
Then again he might be wiser if he does, if he keeps her alive he will either have to come up with a reason why MC would allow her back in his life in a way Deb could be happy despite what happened and Milly would also have to agree. After what has happened I cannot see MC choosing anyone above Millie's interest first whoever she may be from his past and before he will be even able to start thinking about forgiving Deb
he has a lot of stadia to go through and even then forgetting will be likely impossible, let alone her regain enough of his trust. This will be almost impossible after what happened. A happy Deb seems not really an option, at best a tolerated and unhappy one.
Or he will have to make her an enemy after what happened and how her brother kind of naturally reacts to that, which her fans might not like either, a really evil Deb. Let alone those of us who were not really a fan of her earlier, due to her actions and that past.
Either way dev has his work cut out if he keeps her alive.