Hopefully, in the timescale of 10,000 years, we'll have refined plastic eating bacteria and the like to get rid of microplastics. It makes more sense to worry about a 20-100 years timescale.
https://aem.asm.org/content/77/22/7962
I expect they'll be common well before 10,000 years. It's certainly an easier problem than getting CO2 out of the atmosphere.
Typically all you need to do to keep microorganisms from eating something is keep it dry. We tend to do that for laptops anyway.
Besides, the assertion wasn't that plastic would still be useful for everything. It just wouldn't be useless.