How many months can I leave Bolivia without losing my residency?

Hi, I am currently in Santa Cruz and waiting for my 1 year missionary residency. I can pick up my passport in 2 weeks and only need to apply for my carnet after this. However I have been ill and may have to return to England for 3 months to get better. If I do this, can I return after these 3 months and carry on with my 1 year residency? If 3 months is too long to be out of the country, how many months am I allowed to leave the country for before my visa is cancelled?
Thanks.