Days has a very bad habit of killing characters (writer A), then later needing/wanting the character back (writer B, C, D) so they invent ways to do have the character alive again. And this is what happens when Corday pays no attention, allows the characters' demise, & Days gets ridiculous with all the walking dead inhabiting the town.
As to returning after saying they won't ever be back.....yep. Louise Sorel (Viv) got really ticked off a few years back, said she was done with Days, would not ever return. Camilla Banus (Gabi) has left, Kate Mansi (Abby), Peter Reckell (who did return, but when he left last time, it was evidently for keeps), Kristian Alfonso (Hope) has left twice & returned. These were all of their own volition.
Muzza is right about Lexie, who like Bo, said they wanted to leave for keeps, and meant it. Yes, the younger actors particularly want to do other things, try something else. But it is Corday who should be keeping an eye on what is going on, and put his foot down on the "deaths" of some characters. They could easily move away, take a job elsewhere, join Doctors without Borders, Salvation Army, touring stage company, become a fishing or hunting guide, design furniture, write for the movies. LOLOL