No, it was declared insolvent on Jan 26th. Today (Feb 26th) is the deadline for creditors (that would be including Devs that were never paid for their OS4 work) to file with Bert with their statement on what Hyperion owes them. March 4th is when Bert compiles everything and presents a report on what to do with Hyperion (including liquidation option). If a Dev does not file in a few hours, Hyperion is then free from ever having to pay that Dev for their work.
I don't know Belgian law, but it doesn't work like that any place I know about and it'd be very odd (though possible) for Belgium to deviate substantially from most European countries in this respect.
A creditor that does not file a claim with the administrator will have severely reduced chance of getting a piece of the pie *if* Hyperion is liquidated, but only because in the case of liquidation the assets are irreversibly (for the most part) sold of or distributed to creditors, and the company (and hence the debt) ceases to exist at the end of the process. A claim does not just evaporate into thin air because a time limit set by the bankruptcy court passes (though depending on jurisdiction the difficulty in getting a claim recognised subsequently may vary)
If the company is not liquidated, claims are generally not affected at all any more than other contracts would be - the company would in that case generally go back to operating as if nothing had happened.
Now Ben has filed an appeal against the original (default) ruling. However if the courts grant Ben another hearing, all Bert's work is going to be momentum working against Hyperion especially after the financial audit and all the debt that I doubt was ever included in Hyperion's book such as debt owed to Devs. It's going to take a miracle.
What you are suggesting is that you doubt that Hyperion has followed the law. If you are right, and there are debts owed to Devs or others that is valid, and that does not appear on Hyperions books, they've carried out accounting fraud to an extent that would be a criminal offence in most countries.
Just to make clear what we are talking about. If a lot of unknown debt surfaces, then that's far, far more serious than a bankruptcy claim - a bankruptcy only very rarely gives rise to criminal liabilities for the principals of the business (they main way that would happen would be if the principals of the business have known for some time that the business was insolvent without starting insolvency proceedings).
Unless you have something more concrete than unspecified "doubts" about their bookkeeping, that is speculation of a level best left until after we see what actually happens.