Comment 32 for bug 1219337

/*
 * Info stored in tty ticket from stat(2) to help with tty matching.
 */
static struct tty_info {
    dev_t dev; /* ID of device tty resides on */
    dev_t rdev; /* tty device ID */
    ino_t ino; /* tty inode number */
    struct timeval ctime; /* tty inode change time */
} tty_info;

That is the info required.
Yes, if you leave your terminal open, the pty is still there.

Debian hasn't fixed this in squeeze or wheezy yet, it's fixed in jessie because they have a recent enough version of sudo.

We do plan on backporting monolithic timer support, we just have not had time yet.