You will be able to maintain a low bodyfat without tren if you will stick to a strict diet and cardio, but you might lose definition, hardness and ofc muscle mass.
On the other you actually can keep the hardness with enough Masteron.
Understood, what I'm asking is once I've dieted down while ON tren, how much of the fat loss can I hang onto once I get OFF
It's really up to you, you can even pop some clen, t3 and other fat burners and get even leaner.