I consider riding alone safer than riding in a pack. Packs do unpredictable things.

I have found that it is easier to get a ride if you have a broken bike than it is without. So far I have tried it in France, Sweden and the US. I think it is even easier on a broken sports bike and if you are wearing a colour-coordinated set of bike shirt and spandex bike shorts.

As plan B bring a cell-phone and enough money to get home. Public transit is usually not very far away and if you are on a moutain bike you probably have shoes that are ok to walk in.

If you do not know how to fix a flat, dont worry. It will just take you a bit longer to get home than if you know how to do it, and you will not get the hours on the bike you had planned. Just as is the case with the more infrequent mechanical troubles (I have been haunted by broken spokes the last 2 years).