Ideally every organization would have their replacements trained and ready to step in when their leaders leave. In theory, if the president of an organization steps down, the vice president is ready and able to step up and step in.
Realistically, smaller organizations frequently can’t afford to have the the replacements for their leaders on staff. They might not have enough funding or other resources to do that.
The key is, to have a short list ready of potential replacements for key individuals. These potential replacements wouldn’t have committed to anything and might not even know they are on the short list but having the short list readily available is vital for successful succession.
Starting the look for a replacement when the position needs to be filled is way too late, in order to be properly prepared, you have to be planning for these situations far in advance.
Have a great day!