I have integrated Paypal payment method, and after success transaction it redirects to success URL where function/query updated database with the transaction data.
My question is if just after success transaction from Paypal account(money withdraw from account) user's Internet goes down or if he closes browser (before redirecting to success URL where query updating db query runs), will his/her transaction data be saved in database? Or how to handle such situation?
You do not need to worry about this issue if you use PayPal IPN. Even if user's Internet goes down or he/she close ths browser, data will still be transitted to your IPN URL. You can refer to the link below for the details.
https://developer.paypal.com/docs/classic/ipn/integration-guide/IPNIntro/