There is a big difference between 'low quality' samples and 'low grade' samples. I know it has been said before, but most samples are bloody awful because of the 'creative liberties' taken with the original sounds, ie normalisation, tuning, noise reduction etc. I recorded the 3-violins from #996 warts and all and programmed it into a sampler and I can absolutely guarantee you that there is no way this side of a miracle you could tell it from the real deal. Comparing that to what M-Tronfirst produced and you have to wonder what they were even thinking about. I haven't had the chance to see or feel the latest batch but they sound a lot better, it must be said.
I'm absolutely certain that one day Mellotrons will turn no more, but given that it'sthat sound that we are after you realise that the instrument is only the medium for the noise that it makes. As long as the sound is captured somewhere and can be reproduced by whatever means then it will be around for years and years yet.