As the other posters have already noted, L3 will not loop forever, as TTL precludes that. Of course, when @pman wrote "your router use TTL (Time-to-Live) value in the IP datagram header to avoid Routing Loops." and "Therefore you should not have loops", he meant no "forever" loops, as he too well explained TTL processing in the same section. I.e. transient loops can occur (and often do occur during a L3 topology convergence event).
If fact, assuming in your OP example, some sending source continues to transmit packets, each of those packets will loop between the router and L3 switch until TTL expires, which means the quantity of traffic on the loop transit links will also be increased by the TTL value. Because of that, I suspect, TTL can be initially set less than the possible maximum TTL value, so L3 looping packets can be dropped sooner. Also, of course, if initial TTL value is too small, packet will be dropped before it reaches its destination.
Also, BTW, as @pman mentions L2 switch processing, although he didn't mention frame looping, frames can loop forever (which is why L2 loops are so bad - especially if a sending source keeps providing more of them). To handle a L2 active loop, generally you need to "break" the L2 loop path, which often might entail physically pulling a link out of its port or powering off a switch. (Often, switches in a L2 loop situation are so overloaded, you cannot manage them, as you would normally.)
