There's little accommodation in Lembar and no advantage in staying.
Losmen Tidar
Jl Raya Pelabuhan, Lembar
+62 370 681444
From Rp 50.000
about 300m along the road to the port from the junction with the main road from the city
If you do get stranded, Tidar has five rooms with fan and attached bathrooms, and a restaurant with a small menu of inexpensive Indonesian food.