The vitality of music (and probably the rest of the arts), has always depended on a symbiosis between professional and amateur musicians. Some things still need professionals, such as fielding a top level symphony orchestra. And high caliber teaching.
Among other things, I play large-ensemble jazz. Over the years, I've played in a number of bands, and the level of quality and variety achieved by players with professional training is a noticeable step above amateur players. The material that my current band plays is unplayable without training. About half of the band members have music degrees (many teach music in the public schools) and the other half are dedicated amateurs with past training like myself.
Other styles, like folk music, are essentially sustained by amateurs.
Some things can only be done by amateurs, or professionals who also have a musical hobby, such as playing experimental, obscure, or historical music. Amateur musicians also support the professional scene by attending performances, taking lessons, buying instruments (resulting in economies of scale), etc.