I know it sounds reckless, to continue to track uplift is the responsible thing to do right? But in reality there's an important aspect of optimisation testing that needs to be taken into consideration here. Testing outcome is usually the result of the following variables:
product benefit + moment in time + market position + customer experience
Can you continue to accurately measure and account for each of these factors after you've conducted a test? The honest answer is probably no. Also I don't know many people with the personal bandwidth to monitor every single test once it's finished. If I wanted to double my workload I certainly would!
The important thing to do is ensure is that your test has been given enough testing time and traffic volume in the first place before you conclude the test as this post reasonably states Don't Fool Yourself with A/B Testing. If you've done that you should have a reasonable level of confidence in it's future performance.
If you still want to track uplift after testing I would suggest the following are available options for you:
1. Set up a Google Analytics Goal. This gives you the ability to track the performance of a specific customer journey within your normal web analytic. Yes you have to use Google for this one, but any web metrics tool worth it's salt will have the same functionality.
2. Leave your test running. This to me is the fail-safe option. Once you have a test winner up-weight this in favour of the default content but leave a small percentage of your traffic going to the default as a benchmark for continued performance. I usually leave 5% going to the default for a period of time where possible to ensure I've made the right decision.
3. Run a Follow-up experiment. This is a great feature in Google Optimizer but you can do the same in any other testing tool if you have the resource to do it and there's lingering doubt about the original test outcome.
4. Bespoke tracking. On the pages I optimise I append tracking values to the application form that when submitted to a sales database can be used to tie back sales to a specific landing page. Using this approach you can monitor conversion rate performance before, during and after a test. I cant recommend this approach enough and is entirely dependent upon your on-line application forms particular design as to whether you can implement it.
That's about it really. If I think of any other methods for ongoing tracking I'll add them in.