Megabus is okay. At this time it is one of the more sensible options. You can also check Eurolines. They have similar prices and a lot of connections. Choose what suits you best. Note that Eurolines will drop you near the Brussels North railway station. Megbus stops near the Central station, a stone's throw from the Grand Place. The Central station is a bit better connected to the local public transport network than the North station. But eventually it depends on where you want to go.
Thalys would be a more convenient option (quicker and more comfortable) but significantly more expensive than the bus!
The CEO of the Belgian railways has announced "some solutions" for this week, without specifying which ones ... (Source). Stay tuned!
The promised solution is there. You can read the official relaese in Dutch or French.
As of the 18th of February 2013, there will be two direct IC trains from Brussels to The Hague, taking 2h15 and stopping in Mechelen, Antwerp, Roosendaal, Dordrecht and Rotterdam. As of the 11th of March 2013, there will be 8 daily trains. Due to network congestion, the trains will not continue to Amsterdam. Travelers to Amsterdam have to change trains in the Dutch capital. During the weekends the trains will only run from Antwerp to The Hague, due to works on the Brussels-Antwerp line.
A light a the end of the tunnel? Wait and see. In Summer there will be a final decision.