Upgrading from 1.3.9h / PHP

We are in the process of upgrading our Zen Cart to the latest version, but unfortunately have not completed the process yet. Our site is currently running on 1.3.9h.

PHP 5.3 is being removed from the server our website is hosted on today, and we have been told that our Zen Cart store won't run on PHP 5.4 and our sites are likely to go offline.

We hope to complete the upgrade to the latest version of Zen Cart within the next week, but in the meantime is there anything we can do to stop our site going offline?

I have searched, and found that there were patches available for a similar issues for sites running on 1.3.8 and PHP 5.3, but cannot find any similar thread for our situation - http://www.zen-cart.com/showthread.php?140960-PHP-5-3-Support-for-v1-3-8-a

Thanks in advance for any help.

A number of things come to mind, but none of them exactly fix the issue. First of all/important is that you at least make backups of everything, files and database (export the database(s)). Experience has shown, don't change any of your existing product through ZC as the php version increases, this results in data loss when saving the product. Downloads may not work (issue recently seen).

Beyond all of that, I see various options available: put one or more people onto the task of upgrading the site(s) now to the latest ZC version with all plugins and functionality equivalent to your existing store(s). There are things that could be done also just to keep the store operational, but perhaps at limited capability (not all plugins installed, maybe even an odd-ball template, maybe all sites start with the same template with the desired template to follow)...

It's all a business decision in my opinion, but whatever the case, sounds like to continue doing business in the near future, need to do something or need to provide some sort of notification so that patrons might return again in the future...

You'll probably find that a lot of PHP errors/warnings get triggered when using v1.3.9 against PHP 5.4, because of the many changes in PHP 5.4
It's quite possible that your site may not be using any specific features that would break with PHP 5.4, but that depends on quite a number of factors, which are rather cumbersome to list here.
More helpful would be a list of plugins that you've got on your site, as it's more likely they're what will be the most problematic.
You might also find editing product descriptions in your Admin may blank them out, due to an incompatibility that affects some people.