I closed the tour by accident. Is it gone?
Closing it deliberately marks it as seen, but you can restart it any time from the account menu. If you simply reloaded or lost the tab part-way through, the tour resumes on the step you were on.
From the guide The Guided Tour.
Leaving it, and picking it back up
You are never trapped in it. Skip, the X in the corner of the card, and the Escape key all end the tour immediately, on any step. Clicking outside the card does not — a tour this long should not end because of a stray click.
If you reload the page or close the tab part-way through, the tour picks up on the step you left off at rather than starting over. Once you finish or leave it deliberately, it does not come back on its own.
Read the whole guide: The Guided Tour