If a guy wants to have sex again withdrawing before he comes and after wiping himself after first time just with a moist tissue.pregnancy possible?

YES: Sperm are pretty hardy little things and they are contained in the fluid secreted even before ejaculation. Before, during and after ejaculation you can father a child. Use condoms and spermacide or birth control or welcome to fatherhood.

Yes so be careful: Withdrawal contraception has a very high failure rate of 25-40% per year. Some couples are very effective using it but overall, the success is low. If you do not want a pregnancy then other methods are significantly more effective. Dr harris correctly indicated that sperm can live for extended time periods and some come out before full ejaculation. Be careful :).