Ok. So you survive the gank, and are down 300 hp. You take 50 seconds to heal up the 300 hp with your RoH. it sucks, and you miss out on farm.
So, pop quiz. Exact same thing happens and you don't have a RoH. Wtf do you do?
1- Use 3 tango charges. All in all, it takes you more than 50 seconds to fully heal. Why? Do the math. Tango doesn't start working until you activate it and click on a tree. You get hit in the middle of lane, you get stunned, the gank attempt proceeds, you run out, you can't stop at the first tree because you still need to run, so you run behind your tower and then you activate tango. Time elapsed: maybe 10 seconds. But during that 10 seconds, if you had a RoH, you would have already regenerated 50 hp. It's a huge head start. Ultimately, to regen all your hp, you need to activate 3 whole tango, spend 90g to replace them if necessary, and still didn't save any significant real time.
2- Walk back and heal. This is obviously even worse than 1.
3- Teleport out and heal. More expensive than 1, and will take more time to walk back.
4- Realize you didn't do the math, and while it sucks to sit back for 50 seconds and heal using a RoH, it isn't really any worse than the alternatives.