If I install an outright version of Lightroom6 on 2 computers (desktop+laptop) and my laptop crashes (hope it won't). Can I install Lightroom on a new (different) laptop ? Or will I be locked with the two installation already done ?
You might have to contact Adobe and explain the situation, that one computer failed before you had the chance to Deactivate LR but other than that you shouldn't have a problem.
Unlike installing an operating system on a computer other software is not normally Tied to that particular computer. Meaning if you deactivate it on one computer you can install it on another. In fact I think Adobe software has a remedy for this. If you Sign Out on one system it signs you out on both. So all you'd have to do is Sign back in on the new computer then sign back in on the one that didn't fail.
You can, but you’ll need to start a Chat session with Adobe so they can deactivate the defunct computer and free up the activation for use on the new computer.