Tier2 general extension and dependents travel with old visa.

Hi,

I am new to the forum. Apologies if this topic is discussed already.
I have Tier 2 general visa valid till 14th July 2016 and my wife have dependent visa till the same date. I need to apply for Tier 2 general extension after that. My company is doing that and I have already asked them to do it. They will be applying it next week. My wife need to extend her dependent visa once I have my new BRP card. My vacation plan comes in-between that now, which is from May 21 to June 12. Most probably my wife won't be able to apply for her dependent visa before our travel. Is it legal to travel outside UK with main applicant on new visa and dependent on old visa(still valid)? We are afraid that while coming back to UK on June 12th , border agency might stop her from entering UK. Please advise.

Thanks in advance!
Ginish

Found this link which is discussing about the same issue and a response from home office case worker. Hope this helps someone with same question.

G