In present situation

In present situation, the common scenario in many of the organizations is that the success of any project is the combination of the efforts of the whole team
which includes project lead, project manager, and team members.
On the contrary, failure will be mostly associated with the higher authorities or the senior management.
I personally feel that Project sponsor is not only the sponsor but also works like a project reviewer, project communicator and project champion.
By this it is clear that he or she plays a major role and is the key responsible person towards the success of the project.
The path of the project could be in right direction based on the good actions and decisions of the project sponsor.
Therefore, project sponsor could be mainly responsible for the success or failure of the project as he or she has the key role in delivering and executing the project in most successful manner.