1. No they don't. Spreading at sub-FTL requires redundant self-correcting technology which can run for thousands of years without breaking down. This is about a

1. No they don't. Spreading at sub-FTL requires redundant self-correcting technology which can run for thousands of years without breaking down. This is about as achievable as FTL. Nothing lasts for thousands of years in deep space without being abraded, fried, nuked, or physically stressed to breaking point. 1b. Assuming you can solve 1. with some kind of magical alchemical spares-generating technology that never fails, the technology also has to be politically and philosophically stable, with reliable and persistent goals. Otherwise you'll get offshoots competing with each other. Which may mean undermining and perhaps even destroying previous settlements. How much independence is enough? How accurate are your initial models going to be? 2. We don't know that for sure. Absence of evidence is not evidence of absence. (We do know weird things happen, but we're not putting any serious effort into researching them, so we don't know what they are.) 3. There's no need to think about this after 1. and 2. Edit: to put this in context, you don't need to launch a probe. You need to launch a complete perfectly self-reproducing error-free space program. Which can also adapt to local resources. This seems... difficult.