Is this perma structure still crawler-friendly?

Normally, a slash at the end would indicate that the uri points to a directory (and so find the actual page, is it index.html?, etc). Without a slash would mean that that’s the file’s actual name.
So, that makes sense to me (and maybe preferable to an ending slash). But, you know, don’t take that as gospel or anything. ??

The mod rewrites are all handled server side, if you can type the uri into a web browser and have it load up a page, the crawler will pick it up.
However, I would probably recommend not using that structure. It is possible that you could end up with two posts that have the same name. I have over 600 posts, it really wouldn’t surprise me if my creative titling duplicated itself at some point in them. In which case, I’m not sure what WordPress will do.

Thank you for that advice. I am inserting the unique id # of the post /archives/%post_id%/%postname%

Of course inserting the unique id # of the post with slashes creates new subdirectory with the name of the unique id, and the postname is the only file in that directory.
/archives/%post_id%/%postname%
creates things like:
/archives/156/The_End_of_the_World
I am still setting up my own install but I’m going with a structure that uses a hyphen instead of a slash to separate the unique id from the post topic, e.g.,
/archives/%post_id%-%postname%
or
/archives/%year%/%monthnum%%day%-%post_id%-%postname%
Assuming this works (and it does work as a regular expression; my only concern is with some WP-specific exclusion) then I will get something like:
/archives/156-The_End_of_the_World
/archives/2003/0315-156-The_End_of_the_World
This is (a) unique; and (b) keeps multiple files in a directory so that I can log in and browse as necessary.