I do it with SCB that holds my account. They need advice slips to show it come s from abroad. Such slips have to be obtained from HQ in Bkk if more than 2 months old which most clearly are. The first time is always the worst time. To smooth things along next year you may wish to visit your bank every month after payment is made to obtai n an advice slip. When you wish to renew you can present the 12 slips to the teller. By the way when I renewed mine couple months back they needed bank statements for 12 months showing the corresponding deposit and imm asked to see who provided the money - in my case, my pension provider. Make it easy for your bank.
If you lose the B then you lose the WP as far as I know. No visa of any descriptio n would invite big trouble not to mentio n an overstay charge of 500 baht a day. Continuing to work could result in jail and deportation at your expense.
The letter I got from the labour office was merely a form showing my WP had been cancelled - nothing to do with tax. Nevertheless my employer(who cancelled it on my behalf) gave me that form too late in the day for me to go to immigration that day to get a Non Imm O based on retirement (I had all the paperwork ready). I went the next morning. I was charged 2 days overstay! Go figureπ
Go to the bank with your print outs and they will do a letter itemizing each month and stating they were IFTs. Letter headed notepaper, signed and stamped. 200B. Another 'guarantee' letter is also needed. I am due next week and I will get the letters from the bank in morning prior to my same day imm visit. All ok last year. Fingers always crossed of course!π