One mobilizer is often drawing the picture of early missionaries who “packed their belongings in a coffin.”
When ActBeyond and others train people in CPM/DMM methodologies, one of the things we talk about is “exit strategy.”
Who’s right?
A lot of this is “attitude.”
Early missionaries packed their belongings in a coffin knowing they weren’t going to last long. Disease, warfare, and other trials filled the region. It wasn’t a commitment to necessarily spend 40, 60, 80 years on the field  The SVM saw nearly 10,000 missionaries go out, many to areas with endemic tropical diseases where they lasted not more than 2 years.
When ActBeyond (and others like us) send people to a place, we are doing so knowing they aren’t likely to die of disease (and warfare is marginally more possible but still less likely). Instead, we are sending them to help catalyze a movement.
But a movement is by definition intended to be led by the local church. (E-3 evangelism is far more effective than E-1). If disciples are making disciples who make disciples who make disciples, as soon as you’re past the first generation you’re past the local missionary. And as soon as you reach 3rd generation, the missionary is far less necessary to the process (and may be a hindrance). If the movement is sustaining 4th generation, the missionary needs to help the movement but may not need to be locally placed.
Just because a missionary has an “exit strategy” doesn’t mean they don’t have a “coffin-committed mindset.”
Even people who only commit to 2 to 4 years can be play a strategic role, however: a point for a different post.