Stabilization during mellowing

To what extent are live organisms needed during the mellowing process?

Is it advisable to sanitize with potassium metabisulfate and potassium sorbate as soon as fermentation has ceased in the secondary fermenter (ie, just before beginning bottle ageing)? After several months of carboy mellowing? Or not at all?

That question is probably moot if calculated ABV is over 10%, but what about ciders fermented without added sugar?