Most churches say that it is good to have an interregnum period in-between one vicar and the next. During this time the church refocuses and re-evaluates its priorities. It is a time when the congregation can look at the skills they possess and they can use these in church life and not need to rely on a vicar to do everything; therefore it is during the interregnum that the church will normally see the most volunteering and the congregation can come together.
At the same time it is a time when the church can decorate/do up the manse to make it ready for the next vicar to move into.
If the church has a funeral it is normal to invite the old vicar to come back specially to do it, unless there are other vicars in the area who have a special link with the church.
My church had an interregnum of three years, and it is generally held that it was a very strong time for the church, and was actually a time of growth. On the other hand a local church had a very short interregnum, chose the wrong vicar and were very unhappy for the short time the vicar was with them, now he has left they are having a longer interregnum.
The timescale will however depend largely on your denomination, if you are a church who chooses their own vicar it will be a longer interregnum than if you are a church assigned a vicar from central office.
Hope I've been helpful.