Keep the deck and continue to use it. If you can get an replacement Devil from the singles bar thread, do, and add it in. It's a popular deck, I believe you won't have a difficult time finding someone with an incomplete Rider Waite who can help.
Any readings you do with the Devil missing, when you need to get that type of message, the cards needed to show you will pop up.
If he wanted to hurt you by making your deck unuseable, and you still use it, then he hasn't won.
Popping in because I had something similar happen. Long term relationship, he was abusive, I left him and left my stuff. He took a knife to my Oracle of Shadows and Light (the original Austrailian printing with the better cardstock, and my favorite non-Tarot deck). Box is damaged, and a lot of the cards have holes in and knife marks on. I eventually got it back. (Quick aside, went completely no contact after I was able to obtain the last of my belongings, and since then he has passed away. It's weird, but please don't feel condolences are necessary.)
So, it hurt. I loved the deck, and I'm in the US, so all the new printings are on inferior cardstock, and I'm broke and can't afford to replace it. Enough of the cards are damaged that I can't tell which card is which when I'm looking at the backs. And... after a while, I didn't feel all sick and broken hearted (about the deck or the guy) when I looked at it. So, I still use it. It works just fine. I still love the deck. I feel guilty, because I sort of personify the deck & characters in it in my head, and it's like they have a boo-boo cos I dated a jerk... but, the deck doesn't seem to mind.
Also, you could send an email to US Games and ask if they'll mail you an extra card. They probably will, for free. They've done it for me when I damaged a card in my Phantasmagoric Theater.
Just my two cents. Sorry your ex is a jerk. Glad he's your ex.