The interests are low now because many states don't invest as much as they used to do. So the demand for money is low. And when the demand for something is low, the price for it goes down.
This has the overall effect of reducing money demand, reducing the premium to get that money (the interest rates continue to drop). Everyone though 0% interest was a hard line and you couldn't go lower, until negative interest rates were introduced to try and reverse this trend, which it largely hasn't.
So yes, these loans will probably be paid, but they will mostly be replaced with new ones.
But no, there is nothing forcing the countries to repay these loans. You can't really collect from sovereign states if they miss loan payments. (https://en.wikipedia.org/wiki/Sovereign_default)
"Repaying" all of that would introduce a money shortage into the economy.
Accumulating too much dept (again as a state), results in a 'trickle up' economy, where a significant proportion of taxpayers money goes directly to the banks (in the form of interest). This is foolish too, since the bulk of the population would not work for the development of society, but for the profits of banks.
>> Is it necessary to pay this money?
It becomes necessary, when you reach a critical level of debt. But I also think it is in the interest of both state and economy that a reasonable proportion of debt exists, as long as it does not exceed a certain level. The big question remaining is, what is this certain level?
...what? No, the money goes back to bondholders, who are themselves taxpayers. I guess banks can make some profit along the way, but it's incredibly misleading to say that the primary beneficiary of interest are banks themselves, or that this is even the primary risk with excess debt.
Domestically, not really. Internationally, it depends on a number of factors. [2]
[1] https://www.lrb.co.uk/v14/n19/wynne-godley/maastricht-and-al...
[2] https://larspsyll.wordpress.com/2017/07/18/the-balanced-budg...