Solar panels slowly degrade and lose both their voltage and current generation maximum. I realize it's only 10-18% but MTBF (Mean Time Between Failure) is a factor never discussed. As in all electrical and electronic components, they will fail. The likelihood of 15 years from now a compatible replacement panel will exist in stock or be available anywhere is Poweball odds. This means an entire system update to all panels and controllers.
There isn’t any technical requirement for a replacement panel to be identical. It only has to be “close”. For example, I added later 80 watt panels to an array composed of 75 watt panels (same photovoltaic type). If the mismatch is too great you will of course have electronic sub-optimizations. If the appearance of the new panels if different you might want to put them at the end or something.