Does anybody know any gameplay differences between the two? Can I play the MP file as single player and still be the same?
IIRC, the main (only?) difference between the solo-versions and the MP-versions of the Firaxis-Scenarios, is that the latter have only 8 Civs
in total; when the solo-versions started with more than that, the more minor Civs were removed, and their towns deleted or donated to the remaining (major) Civs.
But IIRC, RoR had only 8 Civs to start with (Rome vs. Carthage, Greece vs. Persia, Egypt, Celts, Saxons?, Sassanids?), so in this case, I would imagine that the MP-version isn't significantly different from the solo-version. Assuming that it
is only the .biq that you've mislaid, and you still have all the associated RoR-files and -folders in your
../Conquests/Conquests/ directory(?), you should be OK in terms of simply
playing the MP-.biq as a solo game.
However, to get any scores recorded in your "Conquests!" Hall of Fame, some extra steps might be needed.
The game .exe can read that HoF-file to see which Conquests have been completed successfully, and which one(s) should be played next (once you've won all nine, there's a little victory-video, starring Sid Meier!) — so each of the Conquests is numbered (Mesopotamia = 1 ... WWII Pacific = 9; IIRC, RoR is the second Conquest in this sequence).
So first of all, you would likely need to copy the MP-version of the .biq back into the
../Conquests/Conquests/ directory, and you would then likely also need to rename it to match the style of the other solo-version Conquests .biqs (e.g. deleting "MP", adding the number). You may
also need to open that copied/renamed .biq in the Editor, and double-check that the "Scenario Properties" window shows the correct sequence-number.
Failing that, I would be willing to attach a copy of my RoR .biq to a subsequent post or PM (subject to obtaining permission from a friendly Moderator — but since you wouldn't be able to use it without having the game installed, we should be okay under Forum Rules).
As a possible alternative, you might want to have a look at the "Downloads" section for mod-mods of this Scenario. The most recent of these that I know of is
@Nintendohomie's
Chris's Rome Remix, a highly extended version which was designed to replace the original solo-version.