Its bad. There’s actually no telling how long you could go without symptoms since you say you have none now. But basically a bad head gasket means engine death in two senses. One is that with a bad enough breach the engine will run very poorly or not at all because there is no compression. The second is that you’ll end up with oil & coolant mixing in with each other, coolant loss and overheating, and those kinds of things will basically destroy the engine. If you fix it now its still fixable. Wait too long and its scrap metal.