If they died tomorrow (God forbid) it would be pretty easy. When they die 10 years from now... who knows? Replacing built in appliances with something that fits properly in the previous space is going to be a potential problem whether they are paneled or not.

The DW are fairly standard sized, fridges less so. I would imagine columns will be probably easier than a bottom freezer at least.

It will be challenging to find new panels that match perfectly with difficulty depending on style and finish. You might get lucky and be able to reuse the old panels but don't count on it.

On the bright side, integrated appliances all come in stainless finish as well, so assuming you can get an appliance into the hole (like DrB says, the future fridge might give you trouble), you'll be able to get one with a stainless front.

Do you know what brand? Sub-Zero, for example, has kept the sizes consistent. Our 20 year old integrated 48" Sub-Zero (Model 532) died recently. The panels from the old one could be taken and put on a brand new equivalent Sub-Zero (model BI-48) without any problem.