Is it mentioned anywhere if Sanderson will be completed the remaining two prequels? Thanks.

Unknown at this time, Tor wants them to be written, but Brandon and Harriet are hesitant about the idea.

It is rumored that Sanderson would at least do the prequel of Tam finding Rand.

I take it was the Outrigger novels that Harriet and Sanderson was hesitant about, not the prequels.

 

Its all of them, RJ didn't want other people playing in his world, in fact, only in the last year did he decide to let Harriet even keep his notes to finish the main series.

Listen to the 4th age podcast, i think it's episode 45, where they interview Brandon Sanderson and ask him, among alot of stuff, this exacly questions.

 

He says, in short:

 

Prequells? Maybe (special mention to Tam history, but just 'cause it's one that Brandon would like alot)

Outtrigers? Less probable (there are less notes from RJ)

Other Stuff? Never (so no Hawking novel or manetheren or AoL)