Saturating a BJT with an open load
Providing the base current does not exceed the manufacturer's recommendation this should not be a worry. You should calculate base current when the collector is open circuit. This is likely to be the worst case scenario.

One thing to watch for is the switch open-circuiting the relay - I'm not sure how you plan to do this but it might be a good idea to put a reverse connected diode across the relay. In case you weren't aware - when you open-circuit a conducting relay or coil or inductor you will get a small spark that can damage a transistor. If you are using the collector switch correctly this stops most of the problem but it's still worth the small investment.