No none of it helps because all your stating is gibberish nonsense.
What did you email them when you got that email back for starters? No **** you can not teamview to profile that is not active. If you wanted to support someone. If teamviewer is running as s service or you are consoled in when running it then you can teamviewer to it. But no you would not be able to teamviewer in if the software is not running.
This was your question?
"How to use teamviewer if my RDC window is not connected/closed." What was the rest of it? No you would not be able to teamviewer in and help someone that only has remote desktop access to something.. etc.. Since how would they run tv, etc. Which has NOTHING to do if tv is installed as a service on the machine.
So where is the question you asked them in detail?
2) Yeah I do!! Lets say they reboot the router daily, lets say that isp changes the IP address on purpose.. Your still going to be inside a network block of a.b.c.0/mask so there will be a range of ips, be it 254, be it 2k be it 4k, etc. That you will fall into.. So lock it down to this and your done.. This person can only access the remote desktop from that location or if he vpns into that location, or for some crazy reason he lives in the area and has the same ISP.
But a place of business would normally have a static anyway, other than small ma and pop shops with home internet type connections. So I take it this is a ma and pop shop?
b) if you limit the ip range to who can access he wont.
c) makes no matter to the solution allow the netblock as already went over in great detail!
d) Because of how dhcp works, there is a lease time.. You get the IP address for a specific amount of time. Even if you shut off your device that lease is still yours until it expires. Only once the lease has expired does the IP address go back into a pool for reissue. So even if off for length of time, that IP address is still under lease and you will get it back when you comeback online. These leases are normally for hours if not days.
So there is my lease from my router.. Notice the time of the lease 345600 seconds = 4 Days.. So I could turn off my router and would have somewhere short of 4 days before my IP address would be returned. Since you renew it at the 50% would have min of 2 days on the clock. This is how you keep the same address even if dynamic.. You keep renewing it if on, and even if off you need to be off for longer than the lease to loose the Ip address you had. Work you would think would be on 24/7/365 --- keep in mind not talking about your local rfc1918 address that your work dhcp hands out, since this has nothing to do with anything your talking about.
e) already answered in great detail as well - use a netblock
f) Again netblock!!! What do you not understand about a range of addresses? An ISP can only hand you an address they own, so its going to be a very small range.. If you see in the above lease.
option subnet-mask 255.255.248.0;
so /21 or 2046 addresses.. How is that not good enough restriction??
g) more gibberish!
edit: Here you go - look accessing via tv, remote desktop not running. Can access whatever profile I want, etc. So your problem with what tv sent you was how you asked the question. Because clearly I am remoted to this machine, can login to whatever profile would be available on the machine and remote desktop is not running - look no 3389 port even listening
So here I now see it on my computers TV interface of machines I can connect too.
Here is the windows login screen where I could pick what account I want to access.
Here is me connected via tv, when clearly remote desktop is not running on this machine!
So how is that remote desktop has to be running for TV to work??