Typically in past expansion drafts young prospects would be exempt to a certain age or to a certain amount of years they've been professionals (two or three). If it's two years (most likely scenario) for this year Miller and McIlrath would be automatically protected--for next year they wouldn't. Fast with one year pro would still be protected next year.
Almost all teams are going to opt for protecting 1 goalie, 5 defensemen, 9 forwards. There would be some chance we would lose Talbot but there would be a number of goalies available.
If there were 4 franchises at one time we would probably lose 5-6 players. If there were two teams it would be around 3. I really don't see 4 teams coming in at once. Apart from 1968 when the NHL doubled it's size from 6 to 12 teams the only other time more than two teams came on board at the same time was after the WHA collapsed. Edmonton, Hartford (Carolina), Winnipeg (Phoenix), Quebec City (Colorado)--former WHA franchises came into the NHL then. I might be missing someone. Those teams if I remember correctly were allowed to keep some of their own players--for instance Wayne Gretzky had signed with the Indianapolis Racers when he was 16 or 17 and had never been drafted by an NHL team. The Racers had shortly thereafter traded him to the WHA version of the Edmonton Oilers where he'd played a couple seasons already. Edmonton was allowed to keep him.
IMO if the NHL decides to expand again--they will expand two teams and the likelihood is stronger that they'll expand out west and even out the conferences to 16 teams apiece. Currently with 8 teams out of 14 making the playoffs out west and 8 out of 16 in the east it would balance things out. Typically the NHL regular season schedule has also expanded with expansion. Anyway there are places out west--Seattle, Las Vegas, Portland Ore., San Diego, Milwaukee that could handle an NHL team. In the east I know Quebec City is very much wanting a team--there have been rumors about Hamilton Ont. or another team in the Toronto metropolitan area.
Which brings us to London, England, Stockholm or Helsinki but if that ever happens it is probably farther down the line than the next few years.