Importance of Siebel Gateway clustering

Hi,

We need your inputs in addressing some of the questions on siebel gateway clustering.

Currently ours is very big implementation having 10 k + users will using siebel application in future. Earlier  due to budget constraints we have not implemented siebel gateway in the initial set up. But now, looking for siebel gateway clustering option for high availability solution.

But in siebel if gateway is down for some time in production , all users can log into siebel. Not only already connected users , even new users can be logged in to siebel application.

Even we can even navigate to all the screes in siebel except server admin.  So in case gateway machine crashes, we can even go for restore in couple of hours, even in that time also users can be connected to application and access eveything.