Tier 1 General Dependant visa extension

Hi
My visa is up for renewal shortly. In order to save money on renewal fee, I was thinking of getting my (main applicant) visa renewed here in UK but getting my dependants (wife + child) visa renewed from India, since the dependant renewal fee is only £874 (outside the UK) and because we are going to India for a holiday in a couple of months anyway.
https://www.gov.uk/tier-1-general/overview

The question is, my wife and child are living with me in UK, So if I only get my own Tier 1 visa renewed in UK and wait for them to go to India in a couple of months - will their existing dependant visa become invalid as soon as I get a new visa or will it remain valid until the expiry date mentioned on it?

Thanks for your replies/advice in advance

Hi Gupta,

I have been searching for similar information but could not find this in the board.

Have you received or gathered any information about this? Would you mind sharing it with me, please.

Gurus:

I have been in UK for more than 3 years but my dependants joined my this January 2013 so It is required for me to maintain funds 1895 funds per each dependant. Am I right with this assumption or should I maintain 630£ per head?

Also, kindly provide your thoughts on which Mr.Gupta has raised in this threaad. My situation is almost similar to him so want to save money.

Thanks in Advance for your help.

Regards,
Upendra.