Beware of unmarked spoilers!
If his illness progressed to the point where there was no chance of recovery, and he was in great pain, it wouldn't be too out of left field for Love to euthanize him. And, as her actions regarding Joe and Forty show, Love feels killing is morally justified if it's done for someone you love. Of course, whether he asked
her to do this or if she just did it without consulting him is a whole other matter...
Delilah will haunt Joe in the third season.
He's haunted by Beck in the second, and Joe seemed to feel even worse about Delilah's death than hers.
Forty will haunt both Joe and Love in the third season.
Love may be evil, but she did love Forty in her own messed up way, and Forty was one of the main links between Love and Joe.
Ellie will come back and kill Love.
Even if she mostly blames Joe for what happened to Delilah, Ellie will realize Love was the one who killed her sister, and she will come back for revenge.
Love's baby isn't Joe's.
In fact, she might not have even been pregnant when she told Joe she was. The timing of The Baby Trap
convenient. It's certainly plausible that it's Joe's, and he doesn't seem to doubt her, but it also wouldn't be too out of left field for Love to claim to be pregnant to keep Joe with her, and then go behind his back and find some other poor schmuck to do the job. If this is the case, and Joe inevitably finds out, that'll get rid of what few qualms he may have had about trying to remove her. Whether he takes it out on the kid remains to be seen (though given his actions towards Paco and Ellie, they have a decent chance of being spared unless he really goes off the deep end
Gabe knows every crime Love has committed.
Because, as he says himself, he has a fantastic bullshit detector. It is possible Love's other friends also know about it.