The Isle of Lewis has public transit. The main tourist sites can be reached by public transit. The "out of the way" places would be difficult to see without a car.
Plenty of places to hire a car and a semi regular bus service to take you round the main roads of the island to see the sights.
I should think the chance of that I should think is zero, be warned Sunday is a complete no go,
Get an answer from Cabarfeidh Hotel staff and past guests.