Assuming that we are correct in guessing that Northern Arizona is seriously contemplating dropping football, this will at least merit serious discussions within the Big Sky membership.
Would they kick NAU out ? In kinda doubt it. There are not a ton of FCS football-playing schools in that footprint.
Here's the list -
Cal Poly (Big West, Great West FC)
UC Davis (Big West, Great West FC)
Southern Utah (Summit, Great West FC)
North Dakota (Independent - perhaps soon to join the Summit, Great West FC)
South Dakota (ditto)
North Dakota State (Summit, MVFC)
South Dakota State (ditto)
U of San Diego plays non-scholly football in the Pioneer, I doubt they have the budget to go for more, and the Big Sky would be a travel hassle for San Diego.
Canadian teams could also be a possibility, but I'm not sure the NCAA has formally approved that, as the NAIA has...
Pounder, you mention Sacramento State. What is their long-term plan ? The Big West works well for travel, but has no solution for their football team, so they would seem to have to look at the GWFC, which will have not have an FCS AQ for some time, since North Dakota and South Dakota are still transitioning to D-1, and the GWFC has only 5 teams and is a tad unstable to say the least. I could see Sacramento State and UC Davis jumping up to the WAC in 5-10 years, but they need to have an increase in Athletic budget and facilities to support that. Both schools seem to be upgrading facilities, but on what schedule ?
So the Big Sky could face the loss of a football team, and a full member, and they need to make contingency plans now.
Some thought on candidates -
Southern Utah - would join in a heartbeat. The Big Sky claimed to have issues with their Academics. That's a convenient excuse, when it suits them. If needed, their academics could suddenly show "remarkable improvement".
Denver - no football, no plans for football. If NAU allowed to remain in the conference with no football, then the Big Sky has changed the rules, and Denver is no longer disqualified. Denver is inside the footprint, and I think they would join (they are looking for a western conference (not the Summit) since the Sun-Belt would rather they move on). IF NAU remains in the Big Sky without football, adding SUU and Denver would give 9 FB schools (8 opponents) and 11 for other sports (10 opponents). That may actually work out nicely.
NDSU / SDSU - should be happy in the MVFC (probably face a nasty exit fee to leave), might prefer the Big Sky over the Summit for other sports, however the Summit may work out well long term, if and when NDU / SDU are added.
North Dakota / South Dakota - no conference entanglements yet. Both schools would certainly join in a heartbeat. Does the Big Sky want 2 schools at this point ? Might they want all 4 Dakota schools in the future IF they lose some surrent members ? Don't know...
California Schools (Cal Poly, UC Davis) - This would provide a better home for their football program. But what else ??? This would also increase travel costs dramatically. I get the feeling that they might be happier staying with the Big West / GWFC up until the time they perhaps contemplate FBS and the WAC. After all, Sacramento State has been studying the attractiveness of the Big West / GWFC combo vs. Big Sky for some time, so the advantages of a compact conference and low travel costs are a serious plus.
My gut feel is that Candidate #1 for Big Sky expansion is Southern Utah. They have football, and are a natural geographic fit. And if NAU drops football, Big Sky expansion will be discussed more seriously.
The problem is that NAU is also likely the main protagonist for SUU joining the conference. Granted, it would be the logical solution to accept SUU and keep NAU in other sports (they would keep 9 in fb for the even number of conference games, but would also have 10 in other sports to have set travel partners). What the BSC really wants though, is to get Cal Poly or UCD in, namely UCD, since they have proximity to Sac State, instead of going there and playing one game, the schools could fly in and out of the same airport and be able to play two games. But Poly also brings in a quality football team, one that has a legitimate chance of ending Montana's stranglehold football-wise. This would also be the logical place to go if either school has aspirations of moving into I-A.
If the BSC does end up kicking out NAU should they drop football, this pretty much eliminates SUU from joining, since they don't really add much to what the conference just got rid of. This might actually increase the pressure for Sac State to move up, to eliminate the southern portion of travel. This could open the door for the Dakota schools to join, and maybe wrestle away the Dakota State schools from the Summit/MVC football. While this definitely widens the footprint, at least if NAU and Sac State are gone it only widens it in one dimension (East-West) instead of widening it east-west and northeast-southwest.