I'm not sure I understand what you mean. Even in the US there are multiple carriers active in every market, and I assume that 3G is competing against LTE as products for the same provider, in the same market. That should mean that LTE subscribers might turn off their LTE to get better call-connect speed, or simply choose a 3G subscription if that functions adequately enough for their general data needs.
That might mean that the big problem will be to convince people to jump to LTE (and the higher price) with slightly worse end-user voice experience. Some customers will, but perhaps many won't. Artificial quality degradation of 3G might be the answer for that, or limiting the 3G-only contract data limits to encourage LTE adoption.
Deutsche Telekom does not offer LTE on prepaid plans. Their minimum contract length is 24 months, and auto-renews for another year at the end of the 24 months. It is not cancellable within the last 90 days of the 24 month period, so if you don't remember to cancel at or before 21 months, you are on the hook for 36 months.
It's also something like 70€/mo for 2GB of LTE. :(
Will they accept a lesser experience than they're used to?
And quite frankly, of course they will. Thats the beauty in having a monopoly on cell phone coverage.