How easy is it to go back to using staggered keyboards?

I use both regularly, no big issue switching. Don't worry.

Initially there was a difference for me, but now I can switch from one to another without a problem if I need to work on laptop keyboard for some reason.

As someone who only types a few words on staggered now and then, I have no problem as long as I look at the keyboard. I would probably need some learning period to write blind again.

Your brain is way more adaptable than you think. I go between 3 or 4 different keyboard layouts regularly and can use them all just fine. I think the secret is just to force yourself to recall locations from memory even if it takes a moment, only look up the layout if you are totally stuck. It's also kinda fun to see how weird of a layout your brain can get used to. E.g. one-handed layouts, morse code, stenography etc.

At first it was pretty hard, but I found that it became easier once I built up muscle memory for my Colemak-DH column stagger split keyboard. Suddenly switching between the split and my MacBook keyboard started working again.

It took me a month to get used to my Corne, mostly because I went split, and 40% (dependent on layers for everything). This was during the pandemic, so I was also WFH and didn’t need to use the laptop keyboard for a couple years.

When my company returned to office, and I started using the laptop occasionally, it took a couple hours to wake up my row-stagger muscle memory, but I’m able to switch between ergo and my laptop without issue.

You’ll be fine. Just be patient as your muscle memory adapts.

I have three different kinds of keyboards. Regular, Alice and split ergo with columnar stagger. It always takes a little while to get back to speed when I switch boards. But I think that the layouts are different enough so that a distinct muscle memory forms for each one. I guess that the most important thing is that you should be fairly proficient with touch typing on a regular board before trying a different layout. If you are still in the phase of learning, I imagine that it gets really frustrating.