I think it's a function of time and effort. Every day you're not in a dedicated developer role, you will lose a tiny bit of "free" updating about what developers do, use, love, hate, etc. You can offset this somewhat by your own efforts, but they will be limited because the process of working with other developers bringing something to production is its own thing, separate from just keeping tech skills sharp.

I've always been quite active with side projects and moved back into development after about 5 years being in management. It went OK. Everyone was younger than me, stuff had obviously changed and I was out of my comfort zone for sure, but it was a successful transition. If I'd not been so into development on the side (i.e. constantly writing tools and apps with new technologies), I feel it would have been pretty difficult to switch back.