Be aware that maintenance is progression as well, as Karin said “it is better than not being active at all”. Also, stats show that if a person does nothing after a certain age, their strength, aerobic endurance, etc. will begin to decline.
For me personally, I try to set benchmarks so that my clients have something to aim for, whether it’s progressing through modified push up variations, a fitness challenge, or body compostion. Try to find something that the person like or has interest in that they could aim for. As we know, without some type of progression the person will plateau which can ultimately lead to no activity.
It also depends on what progression your talking about but as the trainer you have the upper hand; you have the ability to create the exercise program and can progress as needed. You don’t have to revamp the entire program but slowly progress each exerice/component individually.
There might be some other issues that’s out of your scope as well.
Hope this helps, good luck!