If you are talking about whether it is worth continuing to use Tango with D1 after the official support for D1 is gone, I think this is almost the same answer as whether it is worth continuing to use D1. The lack of D1 support for dmd really should not affect how much Tango for D1 is still in use. The real question is: do you want to stick to D1 despite the lack of support or want to switch to D2.
Now, assuming you want to switch to D2 ...
Personally, I would advise first to look at Phobos, because it is a standard library, and although it still has room for improvement, it is much better than for D1. He also has some community support and continues to grow. Newer projects are likely to use Phobos and are more likely to use Tango if they are ported from D1.
However, there is no reason why you cannot use Tango in D2 if you want, especially if you are migrating code from D1. There is a Tango fork that has recently been ported to D2. And, like any third-party library, you can use it in your code if you want. You can even use it with Phobos if you want (unlike D1), although their styles are very different. It really depends on whether you use Phobos or Tango in the first place.
If you are worried that Tango will not be supported in the long run - especially if the official version is still D1-only - I don’t think anyone can really predict this. I expect this to happen, but it would not surprise me if it did not develop much further, simply because most D2 users will use Phobos. Phobos will be supported because it is a standard library. Who knows what will happen to tango. But the D2 plug is currently supported, and it may be that the community will grow around it (whether D1 Tango users will switch to D2 or D2 users, deciding that they want to use it) and this will remain a strong, well-supported library. At the moment, it is simply impossible to find out.
So Phobos is your best bet, but there really is no reason not to use Tango if you want.