The spell does not say, but you should probably appear in a random space
The spell does not say, therefore it is a DM call
you return to an unoccupied space of your choice that you can see within 10 feet of the space you vanished from.
The spell does not say what happens if, when it is time for you to return to the material plane, you are blinded and cannot see. This automatically makes this a situation where the DM will have to decide the result.
Using the random mechanic already in the spell
If a DM was looking for an easy solution to this lack of edge-case coverage, a good one can be found already in the spell description.
The spell does describe what happens when there are no unoccupied spaces within 10 feet of the space you vanished from.
If no unoccupied space is available within that range, you appear in the nearest unoccupied space (chosen at random if more than one space is equally near).
Using this same principle, it would make sense to require the player to return to a random unoccupied space within 10 feet of the space you vanished from. Since they cannot see, they cannot choose (or must choose randomly) a space to return in.
If they are both blind and all the squares within 10 feet are occupied they simply follow the rules as stated and return to a random spot.