The moment is there: Joomla 2.5 has been around for some time now, but its official support will come to an end. On December 31st 2014 (so, the end of this month), Joomla 2.5 will reach its official End-Of-Life (EOL). Here's an overview of what this will mean to you.
A brief history note
Joomla 2.5 came to being on January 20th 2011. Actually, it came a bit earlier: It was released earlier in the form of betas and Release Candidates, while actually its predecessors shared the same architecture for the most part. So, Joomla 2.5 has been with us now for almost 4 years.
In 2012, Joomla 3 was released with a lot of enhancements and new features. Since then, Joomla 3 has become stable and evolved into a much friendlier and usable system. When you are maintaining two different types of products (Joomla 2.5 and Joomla 3) while one is up to date (Joomla 3) and one is not (Joomla 2.5), it is common sense to decide one day to drop the outdated one. This day has been known for quite some time already and this day is December 31st 2014.
The Meaning of End-Of-Life
After December 31st 2014, Joomla will drop Joomla 2.5 development. Joomla 2.5 will be End-Of-Life. The Joomla world will focus on Joomla 3 only and will mark Joomla 2.5 as outdated. If a Joomla 2.5 security issue occurs after that, there will be most likely a fix. If another Joomla 2.5 issue is found, there will most likely be no fix at all - it is unsupported.
Running a Joomla site on an unsupported Joomla version might sounds doable: If no issue occurs, everything runs fine. You are completely right: If nothing happens, nothing happens. However, you probably also run a backup of the website. Why would you do that? Most likely to prepare for disaster. Having no backup of your site is similar to running an unsupported Joomla version: When nothing happens, everything is fine. However, when a disaster strikes, you might need that backup very badly. Similarly, when Joomla crashes for some reason, there might not be a Joomla 2.5 fix anymore, and you might need to upgrade in a rush. And when you are in rush, more things might go wrong.
Staying up to date with Joomla is about insurance: Guaranteeing that you can keep maintaining the website in a proper way.
Should I upgrade to Joomla 3?
Yes. Period. If you are unsure about what this upgrade lead to, simply setup a testing site and use that testing site to see how the upgrade goes. It might be that you simply click on Upgrade and minutes later your site is upgraded. It might also be that you need to upgrade a couple of third party extension. But not upgrading things at all, not even in a testing site, will keep you in the dark for no reason.
In the end, there are three possible scenarios for your site: Either you keep it at Joomla 2.5 for the rest of time. Or you shut it down. Or you upgrade it. Even if you don't want to upgrade things right away, take your agenda and look at the schedule of 2015. When do you expect quiet moments? When are you expecting things to be busy? There must be somewhere a single hour available where you can test the upgrade and see how it goes. It will give you some piece of mind.
How about Yireo extensions?
We will maintain support for Joomla 2.5 for some time to come. However, mid 2015, we will also mark Joomla 2.5 as being obsolete ourselves, and stop with providing support for Joomla 2.5 based websites.
For the past year, we have already shifted all our main development to Joomla 3. New extensions are only developed for Joomla 3. Existing extensions are developed first on Joomla 3 and only tested afterwards for Joomla 2.5 compatibility.
Also, we have upgraded all our Joomla 1.6, Joomla 1.7 and Joomla 2.5 sites to Joomla 3. Most of the time we spent on these upgrades, was spent on creating backups and testing sites. In most cases, the Joomla 3 upgrade itself took less than 1 minute. Solving the issues afterwards also took less than half an hour.
If you are still on Joomla 2.5, we would like to join us in upgrading to Joomla 3. It is definitely worth the effort!