401(k) plans limit loans to current employees, and do not loan money to past employees. In fact, if an employee takes a loan from his/her 401(k) account and subsequently leaves or is dismissed (and thus becomes an ex-employee), then the loan must be repaid immediately (or within a short time
30 days? 60 days?), or else the amount still outstanding is reported to the IRS as a distribution from the plan, and thus taxable income to the ex-employee. Penalties will apply if the distribution is deemed to be a premature distribution.
So, your question about taking loans that total more than $50K from more than one 401(k) plan is moot unless you have two or more current jobs and you are a participant in two or more 401(k) plans offered by different employers and the total assets of in your accounts in these multiple currently active 401(k) plans exceed $100K. If you are indeed working so hard (often, only full-time employees can participate in 401(k) plans)
and are a member of these multiple simultaneously active 401(k) plans, then aganju's answer tells you that you cannot take a total of more than $50K in loans from all these 401(k) plans.