It does seem odd / strange / unreasonable for Silverline to not offer an alternative path forward. Totally understand that they can't honor what would be an implied warranty that's now 6-7 years old, also understand that there may be no reasonable grill replacement, but a suggestion for what to do about the tweeter seems like a reasonable ask. Even if the suggestion is to buy two new matching tweeters from someone else.
If I had bought them new from Silverline, and a tweeter had gone 5 years later, I suspect that "nothing can be done, please junk the speakers" would not be an acceptable answer to me.
Can it really be that nothing, like nothing can be done? The post from Fritz does not seem to imply that.