Welcome to the QuickBooks community! If you're looking to convert your QuickBooks Desktop file to QuickBooks Online, I'm happy to share that's a process that's already available. Depending on what year of QuickBooks Desktop Premier you're coming from, you may be able to make the switch yourself right in product. If not, we have a Data Services team that can help you out. I'll include a number of links at the end of this post that you can review at your convenience.
If you're wondering about QuickBooks Desktop being phased out and QuickBooks Online being the only option, I want to assure you that Intuit is still producing and supporting both products at this time and I don't have any word of that changing. We know that each platform has it's purposes and fits different business needs. We always encourage users to go with what works best for them!
Here are the articles I mentioned above. Stop by again if you have more questions. :)
That's another great question, Kat16. Going from QuickBooks Online or QuickBooks Online Accountant to QuickBooks Desktop is a little trickier, but still doable. It's tricky because there isn't a conversion process like there is for going from Desktop to Online. Rather, you can export certain data from Online that can be imported into Desktop, such as lists. From there, you can build your company file for your business so that you can continue working. I've got a few more links here for you that go over the options.