Yeah, this will devolve into another mic vs. DI thread at some point, with the same pro/con arguments made for either side that have been made already many times on this forum.
Generally, my feeling on mic'ing a bass amp for live use depends on the performance environment first and foremost. If you're gigging the local "bucket of blood" bars that attract droves of drunks, and that don't even consider stage and acoustics, then I'd advocate for a DI by itself since you may never be able to appreciate what a mic can do for the sound of the bass. Just a realistic and practical matter.
Where the venue allows the FOH mixer to take advantage of mic or mic+DI, then certainly that is the best option. This generally only exists at the higher levels of professional performance, or in those instances where you are actually able to perform at a proper venue that puts the stage and sound FIRST due to the fact that they are taking great care to accommodate the listening audience (and they DO care about the sound). It also assumes a FOH mixer who knows what the heck he/she is doing.
To say that a pure DI method can "never" capture what a mic delivers is quite untrue IMHO. I'm a broken record on this count, but to achieve a mic'd tone from a pure DI source involves the proper digital capture of the tonal footprint of that cabinet via Impulse Response (IR) technology. The beauty of the IR is that it uses a mic, or multiple mics (both near and far field), to capture the sound of the speaker cabinet AS PROCESSED by whatever microphones, EQs and Preamps you desire.
Thus, if you close mic a bass cabinet (in a studio) with a MD421, and set up a Neumann U87 condenser a few inches (or feet) away (according to your taste), and run that through a beautiful sounding vintage or boutique mic pre, then a properly captured digital cabinet impulse (IR) of this signal path can be used as the source for your direct feed in a live performance environment via hardware that utilizes IRs. In essence, it is the bass cabinet/speaker + mic(s) + quality preamp, all of studio quality and using tried and true studio techniques, that you can take with you and use anywhere, provided you have the digital playback hardware allowing you to use cabinet IRs as the source of your speaker emulation (Fractal Audio AxeFx, Atomic Amplifire, Line 6 Helix, 2 Notes Torpedo, etc.). This opens up sonic possibilities and alternatives that are generally not affordable or practical in a live performance situation.
...so there it is...
The more sophisticated hardware that utilizes IRs also take things a step further by adding tube power amp emulation. Whether this actually makes a significant difference in the final result is a matter of splitting hairs IMHO, especially in a loud venue at the FOH mix position. For most players, taking a DI feed off of your bass head (preamp), into the IR processor, and then onto the FOH console, will get you pretty much everything you need for a mic'd tone via DI.
The use of multiple captured sources (IOW, different IR captures of different speaker cabinets) also allows you to drastically vary the tone of your "virtual" bass rig (cabinet) so that you're not locked into just one sound of one bass rig. This can be very handy for gigs requiring tonal variation, or those who perform in many different formats of music (blues/R&B/rock/pop/metal).
Guitarists have been taking advantage of this technology for years now (and at very highest pro levels of live performance). If you're a bassist who truly wants a pro alternative to live mic'ing your bass rig, then IR tech is the way to go.
JMHO, FWIW, yadda yadda yadda...
