They aren't coming back, forget it. If you want apps through your STB, only option is to upgrade to Android TV based Binge+ STB. It costs way lesser than what it used to during it's launch.
Tata Sky has taken various factors into consideration before discontinuing web apps from TS+ HD STB.
1. It was hanging with web apps
2. Tata Sky+ HD is very old set top box with low hardware specs. It is only suitable for DVR recordings which is why they have also removed Transfer, VOD features
3. Web apps weren't that what you think, they were very basic, in fact unusable and there was no dedicated app store to pick your favorite/liked apps from
They need hardware side support to enable add all the required features which they did and launched an android powered set top box.
Overall, they tried to optimize the STB by removing unrequired and non-working features