Air India's value to Star Alliance is NOT for the ULH nonstop India-North America routes that are pretty much the only longhaul that Air India operates today.
The real value is the spoke access to the Tier 3 cities in India which are increasingly generating more and more demand for longhaul. He who has the codeshare on Air India metal to Kanpur or Vizag or Guwahati will gain by capturing the longhaul traffic share. Right now, its up for grabs at the gateway. Getting Air India (or any other Indian carrier) into Star means that traffic flow is now captive.
The Star carriers know that Air India is not a threat to their bread-and-butter markets to/from India. They need Air India to feed those services. Conversely, Air India knows they cannot serve every market with marginal demand from India as a spoke (while the Star carriers can as a hub). Hence, Star has a value to Air India.
It's all about the feed. Air India isn't a global player and will never be one. There is no threat, other than to Star Alliance's image by association with the dysfunctional Air India brand.