Let's be honest here this would be a real dick move from Geralt as he would allow his friends to die, while if you let Radovid win then a lot of innocent people will die too, but at the very least Geralt will retain his witcher neutrality in that case.
However, I will now explain why doing this is such a dick move:
Roche saved Geralt's life TWICE
Those who never played the Witcher 2 before know that spoilers are ahead.
In the prologue of the 2nd game Roche helps Geralt escape from captivity, as he was accused of killing Foltest, by giving him the key to unchain himself. And while we can argue that he is later using Geralt or that it wasn't the same as just releasing him from his cell it doesn't change the fact that he is still alive thanks to him. If Roche had not helped him then Geralt would have been skinned alive and hanged soon after.
The 2nd time Roche saves Geralt's life is during "Reason of State" itself and a lot of people have no idea how deep this act is.
Roche constantly says that he is willing to sacrifice anything for Temeria. And yet during this quest he springs the trap for Radovid early, just to save Geralt's life, knowing full well that the fate of Temeria hanged on the success of this mission.
This shows how much Geralt truely means to him as he actually put his life above the fate of Temeria in that instance.
Not to mention you can have Roche and Ves help during "The Battle of Kaer Morhen". And when it's over you can talk to them and ask them how to "repay" them for this? In which case Ves will smile and say that they will think of something. Well letting them die soon after would be one hell of a way to "repay" them.
Their death and Dijkstra's betrayal is all Geralt's fault
A lot of people complain that Dijkstra's betrayal comes out of nowhere and is half-assed.
Well actually no it's not. Contrary to what you think he did not intend to betray them from the start. Originally he most likely intended to negotiate with Emhyr and have Redania become a vassal state of Nilfgaard just like Temeria. However, that all changed when Geralt revealed to him Emhyr's weak points.
Dijkstra knew that killing Radovid ment turning over the whole north to the Empire, but after learning of Emhyr's weak points he found a way to win the war even without him. But there were 2 problems, first Radovid had to die either way and second he had to betray his fellow conspirators. Because if Temeria turned over to Nilfgaard he would not be able to win even with the knowledge that Geralt provided.
So yes his betrayal is half-assed, but not because it was poorly written, but because he did not have any time to prepare better. He had to act right there and he had to act fast. This is also why he asks Geralt to leave as he is aware he may lose this fight as it's a rushed plan. If he were planning it from the start then he obviously would have prepared better and Geralt's presence would not make any difference.
Dijkstra is a hypocrite
In a previous conversation he says that he "no longer believes in ideas" yet now he wishes to create a north empire himself.
He also says that "war never solves problems" yet now he wishes to wage war on Nilfgaard himself.
He is also the one who asks Geralt to hang his neutrality in the first place, and help assassinate Radovid, yet now he asks him to act neutral when it's no longer good for him.
Simply put he lost his head after he found a way to become the most powerful man in the nothern kingdoms and if Geralt let's him have his way then everything that follows will be his fault alone.