Will I lose muscle progress?

I'm going to Romania in 12 days and then to Mallorca about a week after. I'm a healthy weight and size - 165cm at 52kg. For the last few months, I've been doing core and ab exercises at home with the intention of tightening my core. I've gained somewhat visible abs in the process - I wouldn't say I'm ripped, but they're good progress to me, and they're visible if I flex (and in certain lighting if I'm not flexing).

Thing is, I'm in the UK right now, and this heat is making it incredibly difficult to do any form of exercise. Usually, I'd get 15-33k steps 5-6 times a week, but with the heatwave, getting above 5k feels impossible unless I wake up at 5am every day. The heat is also demotivating me from doing my at home core exercises.

Up until I leave to go on holiday, I'm doing a strict two meal a day diet with 0% greek yogurt being the main part of those meals (so I have like a yogurt bowl with fruit and chia for one meal and a savory yogurt bowl situation for my other meal). I'm not tracking calories but I'm definitely in a deficit, and in the week leading up to my holiday, I'll be eating smaller portions (the main purpose of this strict diet is to ensure I'll be able to enjoy holiday food without guilt (as well as losing weight right before)).

If I were to stop doing my core exercises (but still did a 3min plank once or twice a day) and no other activity (so like bedrotting or getting 2k-10k steps a day), would my ab progress go away?

I'm really conflicted because I'm quite physically exhausted, partially as a result of my strict diet.

Any input is appreciated.