Dmitry,
I think we were hoping that removing one kidney would prolong your father's
life (which it certainly did, because, if I recall correctly, he was
bleeding?), if not put him into spontaneous remission.
I'm not a doctor, but I think that kidney cancer can spread to the other
kidney.

"Lymph nodes (next to kidney), lung, bone, liver, brain, skin" is what it
says here
<http://www.cancer.org/docroot/CRI/content/CRI_2_4_2X_What_are_the_risk_factors_f
or_metastatic_cancer_67.asp?sitearea=>

It seems to me that since his chest lymph nodes are swollen, it's almost
certainly due to cancer, (unless he had some infection, viral or other) and
he's at risk for spead. I don't know of any way 100% to stop that.
I don't know of any 100% way to know where the cancer is without a bunch of
expensive and potentially cause him to be much worse, tests.
I realize that you want him always, but I don't know of any guaranteed
treatment for kidney cancer.
If you and your Dad were living in the US, he might benefit from being in a
clinical trial.
Many in trials (on treatment or placebo) do better in clinical trials, but
that's to improve symptoms.
If he has no symptoms, at the moment, there doesn't seem to be anything to
treat.

There's some tests mentioned here (to look for mets)
http://www.nlm.nih.gov/medlineplus/ency/article/000516.htm
They also mention bloodwork.
I wonder if that would help you?
Of course, he cannot have them every month. There's risks to having too
many imaging tests.
J