Boiler removal

[badabing64]

I have an Oil Fired Boiler that is unrepairable and hasn't been fired up for nearly a year. We are just getting hot water via the immersion heater for the time being, and are in the process of finding funds to install a new boiler along with upgrading the hot water cylinder etc. Meanwhile the boiler has decided to spring a slow leek that I guess will only get worse. As we're not looking at getting a new system fitted for a while yet my question is:

If I drain down the system, remove the boiler, should I cap off the pipes and refill the system? Or should I leave it empty, do the radiators need to be filled with water or are they ok left dry?

I'm assuming it's still ok to use the immersion heater on the hot water cylinder, is that correct?

Thank you anybody that can help.