[Opserty]

I'd be careful, you'd probably annoy the heck out of your users. People use browser tabs for a reason, it make their browsing quicker, easier and more productive. Furthermore once a page has been sent to the end browser it doesn't use any more server resources so basically having many tabs open is just like clicking a lot of links.

Is there even a reliable way to detect this? What if some accidentally closes the window and then wants to get back on?

Maybe instead you should look at optimising the scripts themselves instead of trying to limit access.

Just my 2 cents