you start losing your conditioning within 2-3 weeks pretty rapidly. but really if your gains are gonna be all gone that fast then you never had gains in the first place.
but so what? muscle and body memory are REAL THINGS. you need to take time off then go for it, it isn't going to be that big a deal. just try and get in consistency long term, that is the key to anything
guys like me and others on here who have lifted for 20 years can take plenty of time off and wouldn't even know it