It is completely possible, I load bp loads for my 45 colt. There are a lot of cartridges still around that were originally bp loads. The metallic cartridge predates smokeless powder, and most cartridges that have a - in them, like 32-20, 44-40, 45-70, & 45-110 were originally bp loads. The first number being the caliber, the second the grains of bp.
Pretty much any cartridge could be loaded with bp, but cartridges designed for smokeless will have a performance drop. Bp is bulkier than smokeless, my 45 colt load is 30 gr of bp under a 250gr cast lead bullet. A smokeless load that approximates this load is only has 11gr of smokeless powder.
A 44 mag or 357 may not have the fps with bp as a factory load may, but duplicating the old loads for the old cartridges can actually show a performance gain over factory smokeless loads for that cartridge. You may only get 38 special performance out of your 357.
There are some different procedures for loading bp as well, but there is a ton of info online, and I think it's lyman that puts out a bp cartridge reloading manual.
The chances of smokeless powder getting banned without bp also getting banned is slim, especially since bp is considered to be an explosive, while smokeless is considered as flammable. But if push comes to shove, bp can be made at home with fairly primitive methods and equipment, although the quality and consistency of commercial bp is more elusive.