statistics about loaning tradeoff It is very likely that Banks have more loans that have been repaid compared to loans that have not been repaid. Otherwise the bank would lose money instead of money. (otherwise the bank will go bankrupt)

Are there statistics (research papers with references) about this?
(Can be of any country or individual bank etc.)
Loans that have not been repaid are generally called "non-performing loans" or NPL. Each country's bank regulatory body should have statistics on this. Here's one from the World Bank.

Note that this is the ratio between outstanding NPL and total outstanding loans. The ratio could go down if the borrower agrees to continue paying back, or if the banks decide to "write off" the loans. It could also go down if there's a significant increase in loans (the denominator).

Since this statistic is a "stock" variable, the NPL to outstanding loans ratio could be huge, for example, after a financial crisis and stays high as NPLs got "stuck" in the system. It wouldn't be until these borrowers can pay back or banks write off that outstanding NPL could go down.

One way to rectify this is to look at the "vintage" of loans, essentially asking, of all loans originated in 2012, how much has turned into NPL after X months.