The US government is unlikely to carpet bomb its own territory even after hypothetically sliding into tyranny because it would presumably want territory to rule afterwards. What is left is intense urban fighting which we’ve seen in Iraq or wilderness fighting in poor terrain like Afghanistan. It doesn’t end quickly so the cost is a deterrent.
I wouldnt suggest anyone willingly enter an armed conflict with the government for a variety of reasons. For example, you are likely being played, after Maos revolution all the revolutionaries got sent to the hills to be worked to death. Another one would be your own information horizon being manipulated, youve just walked into Gretchen whitmers office thinking there is a huge militia ready to follow in your footsteps, you only need to light the match! Violence sucks, blood calls for more blood and errodes the social fabric; there are USSR officials still collecting pensions in exchange for getting out of the way. Or we could get nuked.
So yes, it does require some more forethought than "weve got guns so we are just going to fight the government", however there already exists an understanding of this, evidenced by the fact that they are only catching the mentally stunted in entrapment schemes.
They will do so in war as denying it to their enemy, but not with M.A.D. So ordinary people having guns has nothing to do with war, except as a deterrent.