Depends on lots of things. If you're trying to improve, then obviously it is going to be more difficult if you're only riding every other week. Ideally you'd be taking enough time off the bike to recover properly, but no more - and that is likely to be one or at most two days at a time, rather than seven.

If, however, you're already fit and just trying to keep what you've got, I'd say you could probably do a decent job of that. During the week off you might lose some, even most of the benefot of the previous week's training, but I very much doubt you'd regress further than that.

This is nothing more than an educated guess, of course. I'd be interested to know how it goes.