depends entirely on the condition of the moss, and whether or not the plants had a bug problem...

if they died a natural death (dried out, frost, etc) and the moss is still springy and not decomposing as you touch it, go ahead and use it.

if it's falling apart, mix it in with the soil (it's on its way to being compost anyhow) and use fresh liner.

I bought a brick of 'coir' the coconut shell fiber, and have been using that instead of moss, and it holds up really well (I line wire baskets with it and plant succulents in them, one is two years old, and not breaking down yet)