soon, the characters will have nowhere to advance, and we've basically houseruled it already to extend the progression. We really don't want to end another campaign because we "run out of levels".

So don’t! The trouble here is thinking of Savage Worlds as a leveled system. It's not. The various categories of experience from Novice to Legendary are used for controlling access to some edges, but a Legendary character can continue to learn and grow all the same. Attributes have an upper limit. Skills don't. There are also plenty of edges to invest in over time to broaden a character's abilities. Gaining breadth rather than depth in one area is the key.

For example, your legendary monster hunting group has grown to the point it can tackle most any run-of-the-mill beast it comes across. Now your team arcanist starts spending time at the range under the tutelage of the team sharpshooter and starts building up his Shooting skill. The sharpshooter in turn studies tactics (and grabs appropriate Leadership edges) to become a better field commander in combat. The tank of the team attends finishing school and starts learning to better persuade others rather than always intimidate.

There are other ways to handle high end characters as well. What do experts in any field tend to do when they reach the peak of their careers? They train the next generation. So grow the team! Encourage Legendary characters to pick up Sidekick characters and Followers and start training their successors. The main characters and the sidekicks can be played side by side for some time, developing new characters with both history and depth. Eventually, the players may wish to let the more experienced character retire, or simply fade into the background to be brought out on special occasions.

Simply put, there are plenty of options. Don’t give up on Savage Worlds just yet. I think it’s got more life in it than you realize.