How to route all traffic through a soft router except itself?

Question

(Sorry for my bad English)

Network config:

I have a MikroTik router serves as my main router.

I have two WANs, one is PPPoE, the other is static IP.

I have a soft router (OpenWrt/LEDE) installed on one of my local computers (VMware-based)

Requirement:

I need to route all traffic to the LEDE (192.168.0.101) except itself. I used to put 101 as DHCP gateway, it worked fine, until I restarts the computer which stops the LEDE running. At this moment, the whole network goes down. I need to manually restarts this VM to recover the network.

My alternative thought is to make 101 as the gateway in routes, which could provide failover abilities - if 101 is down, all network clients can find other routes with higher distances. However, if I simply route all 0.0.0.0/0 destinations to 192.168.0.101, it will route 101's traffic to itself as well, and create a loop, which will again set the whole network down.

I have tried to put routing-mark but have no idea how to make it work. My guess should about mangle rules for giving all traffic from 101 a routing-mark, and route everything without this mark to 101, while because of 101 has the mark, it will follow the main table.

After many times of trying and resetting the router, I think that I have to ask for help now :(