My Rottie is very laid back and easy going, and from what I understand about the Bullmastiff from talking with his current owner, he is very sweet and gentle.
However, there are other reasons that a Rottie may be sent to a rescue.
There are many Rottweiler rescue groups where you can find a Rottie to fit into your family.
The large numbers of rescue groups are wonderful news forpeople who hope to adopt a Rottie of their own, but it is sad that there is such an overwhelming need for so many Rottie rescue groups.
If you don't need a purebred Rottie, a mixed breed will be just as loving.