First, a bit of background.
Seven years ago, when Rich Rodriguez took the West Virginia job, nobody was running the spread offense except Tulane and Clemson, and they'd scaled them back after Rodriguez' departure. Today, the spread offense is being run in some form or another by many teams on all levels of Division I.
Bill Stewart was running a single back three wide offense at VMI in 1994-96 and had a tailback that was the talk of IAA despite being at VMI. Stewart was also an offensive coordinator in the Canadian Football League. In case you didn't know, the CFL only has three downs per series, not four and things are much more wide open than ANYTHING Mountaineer fans ever saw at WVU under Rodriguez. (And it gets a tad colder in Canada than it does in Morgantown.)
With that history in mind, it shouldn't be difficult to see that there are a number of assistants and coordinators in the country that should be prepared to step right in at West Virginia. And with Stewart, whose ego is at least one order of magnitude smaller than Rodriguez', at the helm, there shouldn't be any issues of control to be worried about.
There are coordinators at FCS schools like Appalachian State that would figure to be very interested in a spot at West Virginia. There are position assistants at places like Florida, Texas, Auburn, Alabama, LSU, etc., who would be expected to consider a promotion to a coordinator slot at well.
There are position coaches at schools in the south like Troy (which just won the Sun Belt), Florida Atlantic, etc., who would love to have a position job at a BCS school, and who also bring southern recruiting ties.
There are guys like former Auburn QB Dameyune Craig, the quarterbacks coach at Tuskeegee, who was reportedly set to be Terry Bowden's QB coach if he had been hired at WVU, who still would be interested.
I'd look to Appalachian State, too. Scott Satterfield ('96 Appy State) has nine years' coaching for the FCS version of the Mountaineers. Three straight NCAA 1-AA Championships, and all running a spread offense learned directly from WVU staff. Appy State's past two quarterbacks earned first team All American honors, and the current signalcaller was a third team All American pick as sophomore. Sounds like they know how to run the offense.
I'd look to Tulsa for Gus Malzahn or Herb Hand. That duo ran the offense under former WVU assistant coach Todd Graham, which runs WVU's except that they throw the ball. Malzahn could open new recruiting grounds in Oklahoma and Arkansas, while Hand is a roven recruiter, having headed WVU's efforts while he was with the Mountaineers.
I'd look to Louisiana-Lafayette for a running back coach. Brian Jenkins, in his seventh year at ULL, might be a strong candidate. He has pro experience as well, and could replace Calvin Magee as a WVU recuriter in New Orleans and south Florida.
Need someone to continue to spice up the passing game? What about Matt Mumme of New Mexico State? Mumme coaches under his father Hal ,and played for him at Kentucky and at Valdosta State. He will be starting his fourth year at NMSU in 2008. The Aggies were fourth in the country in passing offense in 2007 and Hal Mumme's offense is well known for its wide open attack.
For offensive line I'd look at Mike Markuson, Houston Nutt's offensive line and running game coordinator at Arkansas. Markuson started at Arkansas in 1998 after a one year stint as Boise State offensive coordinator (1997). He couls also open inroads to recruiting in Alabama and Mississippi.
The hires Stewart makes to fill the vacancies on the staff will be critical ones. WVU needs a coupld of good recruiters to take the place of those departed (not to mention Stewart, who, as head coach, will be limited in the number of contacts he can make. The offensive coordinator spot will also be particulary important. However, the loss of several coaches to Michigan doesn't have to be a negative. Stewart will have the chance to reload with some of his own people, and will do wo with a loaded cupboard of players, expecially on the offensive side of the ball.