Can the bot send a reminder if the customer does not reply, and close after that?
Yes: "If no reply" in Flow settings or on a question sets a reminder after X minutes, an optional closing message after Y more, then the run closes.
Yes. Open Flow settings → If no reply, or the same section on a single question to override it for that step. You set four things: after how many minutes to send a reminder, the reminder text, after how many more minutes to close the run, and an optional closing message the customer receives at that moment.
The close touches only the conversation: the run ends, the lead or deal keeps its stage, nothing is changed in the CRM. The customer is not locked out either: a message that arrives after the close starts the flow again from the beginning. The reminder and the closing message are recorded as the bot's own messages, so they never count as a colleague taking over.