1. Should I continue with consumer court case as builder is under liquidation.
Do not withdraw the consumer case at this stage, you may proceed with the case and get a favorable order and then initiate process for executing the consume court award.
2. Since land owner got the award do I have any rights on the land. I have a sale agreement signed by the builder (through GPA).
The agreement was made while the GPA was effective, therefore the sale agreement is binding on the land owner on this date since he had given GPA to the builder and he is liable for the actions of his power agent.
3. Should I join the liquidation process in Mumbai and ask for my money? Will I get anything if I take this approach.
If there are any possibilities for an expeditious settlement, you may try hat route too or else you may stick to consumer case already in process.
4. As a buyer do I have any other option
As a buyer since you have opted for cancellation and refund, you may proceed in that direction itself.