From https://www.iii.org/fact-statistic/facts-statistics-industry... it seems insurance companies add about 20% to the cost of healthcare.
https://www.politifact.com/truth-o-meter/statements/2017/sep... says 12%.
The same article says Medicare is 2% with the assistance of industry groups, but would cost more without them.
So, abolishing insurance companies would save maybe 5%. That's not zero, but it's not exactly a lot, and would not come close to what's needed.