Relax; since your avocado was grown from seed, even if it was killed down to the ground the roots usually send up a sucker that will make a tree the same size by the end of next year. Put some manure around the base of it to help it along, and look for some life around April.

Another thing you can do is let the new sprout(s) grow and after a few years learn how to graft and graft a favorite variety(s) on. Since you're local to me, I can tell you that there are California Rare Fruit Grower meetings each month where you can learn to graft or even find someone to do it for you. If you don't have room in your yard for two avocado trees, you could dig this one up and put it back into a 5 gallon container. If you do that keep it in a fairly shady cool spot until it's growing well, and keep the sun from hitting the container and baking the roots(wrap something white or reflective around the container). I have a Fuerte avocado that I planted a month ago. I kept it in it's container for a year so it was a lot stronger and healthier looking than the one I see in your first picture. I planted it in a spot where a tree would shade it from the strong afternoon sun, and when I heard about the first heat wave coming I put shade cloth over it. I also wrapped the trunk with an extra layer of shade cloth (I should have also painted it white but haven't done this yet). And I've been diligent about watering it, almost every day when the weather is real hot. And since I've read that Avocado trees like humidity, I try to spray or mist the leaves every day when it's hot. The other thing I'm going to do it put 4 inches of mulch around it's base (but not touching the trunk) to keep the it's roots as cool as possible. Avocado trees have shallow roots and the mulch can help keep them happy and healthy. So far my avocado is looking pretty good. I don't like to water it every day, but with this heat I've decided to take the risk of root rot...and if the heat lets up I start skipping days to let the soil dry out a bit.

i probably wouldnt be in a hurry to do anything ... other than properly water ... let the plant settle down ... and recover .... in tree time... there is no hurry ... its severely stressed.. not hungry ....personally.. i dont fert stressed plants ... do observe if the tips continue to brown ... if they do.. i would consider cutting down into unaffected tissue .... but again ... whats the hurry unless it increases dramatically ... without pix of the whole plants .... it seems like you might be able to grow them a bit stronger ... if you want help in the direction.. we would need those pix .. what your media is.. how you water.. etc ... all the info ... there are other forums that might have more peeps growing AV ... but i havent had enough coffee to recall which those might be ... unless there is an avocado forum ... container forum ... houseplant forum.. etc ... you never know where you will find the muse that speaks to you ... ken

To be honest, after this coming heat, I would re-pot if it was me. I strongly urge you to watch the YouTube on Avocados Gary's Best at Laguna Hills Nursery. The soil that all avocados come in is not good long term. No wood/compost should be in the root zone. Most CA Avo trees are grown by Four Winds. It comes in all ground bark and wood. It rots with water, so you are always on the verge of drought or flood and it will develop root rot. Avocados love sandy soil with lots of water. If you want to keep it in the current pot, make sure it is in shade from noon on and ad a 1/4" gypsum over the top of the soil. Water it when the soil is dry 2-3 inches down. But the best would be a half wine barrel, holes in the bottom, with the blend Gary recommends on the you tube stream.