Hello,
I am training for a cycling event but I have a 4 day long trip without access to a bike, about two weeks before the event.
I would like to ask here, how much of the detraining would be stopped by running.
I could probably benefit from some rest, as I have had some intense training weeks lately.
So, should I try running, would there be any point to it, is resting actually the good call?
I would enjoy the time off and rest. You won’t lose any fitness over 4 days. Also if you don’t run normally, it can make you really sore, real quick. At least, that’s what happens when I try to run even a mile.
Are you going to be on your feet and/or walking a lot? If so, again I wouldn’t stress 4 days off and get back to the plan when you return. Try to de stress for a couple days, you’ll be okay.
+1. I wouldn’t introduce new training stimulus two weeks before the race. This goes for weights, running, etc. If have done some running stick to what you have been doing but keep it within the scope of normalcy.
If you feel like you have to do something… some hiking or a brief walk can calm the nerves.
I also agree with @ChefAcB’s advice. If you were a runner I suspect you could get the central adaptations from doing a VO2 max workout on foot, but cycling-specific benefits? Probably not, especially if you’re not a runner.
One thing I’ve done when I’ve had a few unrideable days coming up is to rearrange the week: VO2 max one day, sweetspot the next, have the next few days off, next workout coming back is threshold. But this was in build & base, & I know that I can stack VO2 max & sweetspot together as long as the VO2 max is short & sharp, & the sweetspot is lower intensity but longer. Workout alternates help here.
I would run because I am an ultra runner first, and enjoy running. But, not because of detraining. You aren’t going to lose any fitness in 4 days.
Echoing what other athletes here have said, you won’t lose any fitness over 4 days – enjoy the extra rest!
Running would probably be counterproductive if you haven’t been doing it lately. It uses different muscles than cycling does, and it can really leave you feeling wrecked afterward. I’ve gotten back into running lately after almost exclusively riding bikes for the last 8ish years… it took me several months to get back into decent running shape without experiencing post-run soreness!
So I’d say skip the running for now, especially as you’re 2 weeks out from your target event. Resting would definitely be more beneficial. 
At the end I went running for half an hour to explore a park, and I had no soreness… And I walked about 20-25k steps a day.
It’s the 5th day today and I am resting today because I feel a bit under the weather, and it’s raining here. Let’s see what happens tomorrow…