I wrote an article on my blog, here which discussed the core membership issue.
I take the most conservative approach that the eight-year D-I membership criterion for becoming a core member starts at the end of the five-year D-I transition period (hence the legendary 13 year wait for the entire NCC, should it decide to go D-I).
Anyway, assuming the Mid-Con takes IPFW, SDSU, and NDSU starting 2007-08, here's what I now calculate as being the core teams for the conference:
2006-07: 7 members--IUPUI, Oakland, Oral Roberts, Southern Utah, UMKC, Valparaiso, Western Illinois
2007-08: 6 members--IUPUI, Oakland, Oral Roberts, SUU, UMKC, Western Illinois (Valpo departs, conference falls below 7-core-member criterion, two-year NCAA auto-bid grace period begins; IPFW's five-year count towards conference continuity begins)
2008-09 to 2009-12: 7 members--Centenary, IUPUI, Oakland, Oral Roberts, SUU, UMKC, WIU (In 2008, Centenary becomes a core member and two-year NCAA grace period gets re-set; SDSU and NDSU become full D-I, starting the eight-year count towards being core-eligible)
2012-13 to 2015-16: 8 members--Centenary, IPFW (begins sixth year of conference membership in 2012), IUPUI, Oakland, Oral Roberts, SUU, UMKC, WIU
2016-17: 10 members--Centenary, IPFW, IUPUI, NDSU (9th year in D-I), Oakland, Oral Roberts, SDSU (9th year in D-I), SUU, UMKC, WIU
So, if my calculations are correct, the earliest the Mid-Con can afford to lose one more core member is the 2010-11 school year--two years prior to IPFW's becoming a core member.
It's possible that the NCAA might bend the 8-year rule to include four of the five transition years (i.e. all but the exploratory year), if the alternative would be to pull the Mid-Con's auto-bid. The NCAA bylaws specifically prohibit waiving of the five-year conference competiton rule but notably does not explicitly prohibit waving the 8-year D-I membership rule. Given how the NCAA rules are currently written, it is possible that if the conference has made moves to maintain their viability, the NCAA might (emphasis might) waive the eight year rule to allow it to keep its autobid, but the first year that becomes a possibility due to NDSU and SDSU is 2013-14 (or possibly 2012-13, depending on how the NCAA views that year of 2007-08 when the SU's would compete in the conference but wouldn't be championship-eligible).
Any way you look at it, the Mid-Con is walking through a membership minefield for at least the next four years or so.
(So, in other words, I pretty much agree completely with star2city . . . )