If I were to be laid off, I'd return them but unwillingly. I have 2 systems from Dell, a corporate phone, and a few other items issued to me. I know for a fact that Dell can simply de-activate your machine's access to VPN's and such and it wouldn't exactly be difficult to wipe the computer clean and start fresh, if you wanted to.
The two systems I have are likely worth a combined $1100 at MOST. The phone is an iphone 10x, which obviously would have it's service cut but, you could theoretically put service onto it yourself (out of your pocket.) That phone is worth maybe 150.. The other device I have is worth closer to 1k I think and is the only thing I'd want to keep if possible. I'd say only about 100 people in the entire company have this device. I'd tell you what it is but I'd give myself away as to what org I'm in and what department I'm in..
But, what if a laid off person was to just not return their computer, badge, etc...?