If there is only one must carry station in the market, then yes that would work temporarily. That actually happened once, when Dish was first subject to the requirement to serve every market. In Salisbury, MD Dish could not come to an agreement with any of the retransmission consent broadcasters. So, Dish launched service there with only one PBS station and a fill-in distant NBC (once Dish got their then-temporary distants license back). The in-market broadcasters complained to the FCC, trying to block the distant station. However, Dish met the requirement to negotiate in "good faith" even though they had not yet actually reached any agreements. So, the market counted as served, and Dish got their longer-term distants license restored.
A similar situation nearly happened again this year, in Erie, PA. Dish had so many simultaneous disputes (or possible upcoming disputes) that there was a very real possibility of the entire Erie locals package being reduced to just one PBS station.
I am not saying that they must come to an agreement, but they must continue to negotiate for carriage. Otherwise, Dish can be found to not be acting in good faith. Of course, once negotiations continue long enough, an agreement will likely actually be reached.
One example where Dish has actually continued to serve a local market without actually carrying any in-market retransmission consent station is Zanesville, OH. This market only has one such station, the NBC affiliate, WHIZ, channel 18. WHIZ has been off Dish since sometime in 2018. The remaining channels in the Zanesville package are a PBS station, and fill-in distants from Columbus. However, Zanesville may be a unique situation, since those Columbus stations are also on the FCC's Significantly Viewed List for Muskingum County, which is the only county in the Zanesville market. This makes those Columbus affiliates the de facto locals for the Zanesville market. Since Significantly Viewed stations also require retransmission consent (unlike distants) Dish may be found to have negotiated in good faith, if they are carrying these fill-in distants as Significantly Viewed stations instead of relying on the distants license. Presumably, negotiations are also continuing in order to attempt to bring back the in-market NBC also.
Interestingly, the NBC affiliate from Columbus is also on the Significantly Viewed List for Muskingum County. However, to bring in a Significantly Viewed station affiliated with the same network as the in-market station, Dish must first reach an agreement to carry the in-market affiliate. So, if successful agreements are reached, Zanesville subscribers could have access to just WHIZ, or both WHIZ and WCMH. Without an agreement with WHIZ, Zanesville subscribers get neither NBC station that serves their area. The real solution, of course, would be for Nielsen to finally decide that Zanesville no longer gets its own separate DMA, and just merge them into the Columbus market. Dish may be biding their time, waiting for that to actually happen.