Those are a lot of what-ifs whereas I've stopped counting the number of third party websites that have come and gone, taking their exclusive objects down with them and leaving route builders trackless. As long as Trainz exists, the owners would have a vested interest in maintaining the DLS....
On the other hand, the DLS does not seem to me to be the Holy Grail of Trainz because it is owned by a private company and they have a tendency to change owners, go bankrupt or complicate the user's life. What will happen to my TRS2019 if the company disappears and the DRM cannot be verified?. What if they decide to charge for everything? So far we have "only" suffered from the very low download speed, so installing a DLS route becomes very complicated.
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Meanwhile, some have been at it for more than 20 years but it's still only a GAME.